Commercially, adventures are a paradox. When you talk to people about what game products they want (especially older gamers who are more likely to be pressed for time) one of the first things they'll say is "Adventures". But, historically, adventures really don't sell well. A recent breakdown from Black Diamond Games runs some numbers that illustrate this pretty well, and also give a decent breakdown of why this is. The biggest reason is obvious in retrospect - in a group of 5 people for a random system, you probably have 4-5 copies of any "core" books. Supplemental books have one likely purchaser (the GM) and usually at least one other likely purchaser (other GMs in the group, or people who dig that particular topic). Adventures have an audience limited entirely to the GM, and only some GMs will buy any adventure for a host of reasons.
Given that adventures are also usually smaller and less expensive, that makes them low-volume, low-margin products. Plus, (and this is more 4e specific) they compete with free material from sources like dungeon magazine. At first glance, that may seem like a reason for an independent person to bother with getting into, but I'd argue that the reality is the opposite for two reasons.
First, while the market for PDFs is not universal, I think people are a lot more open to trying electronic products for things they consider "disposable", like adventures. Second, while a larger company cannot reasonably consider producing a three to five dollar product and still making their nut, a lone enthusiast can do that and make a fair return. The appeal of the 4e market is that even a small slice of it is pretty large on the scale that small game publisher's operate on. Of course, nothing is ever guaranteed, but the point is that as a small publisher looking to publish electronically, the "adventures don't sell" adage is less of a barrier than you might think.
But if you are looking at publishing an adventure there's a lot of baggage to get rid of. There is an idea of a "Standard adventure format" that almost everyone who has played D&D is familiar with. It's a few pages of backstory that may or may not ever come up in play, then a map or three with a number key and each room detailed as an encounter. Add in perhaps one transit zone (an outdoor map with, like, 4 encounters), a random table or two, and an appendix with stats for monsters and treasures, and you're done.
This. Is. Crap.
At this point there are decades of habit attached to this form, and it's easy enough to do not-badly that we will probably never be rid of it, but man, if this is what you're planning to do for your adventure, then just stop for a second and think. Consider the differences between 4e and first edition D&D. Consider the differences between how you play now and how you played back when you started gaming. If it's apparent to you that things have changed drastically over that time, then ask yourself why the adventures haven't.
Now, this is not entirely fair. There have been interesting adventures that have really tried push the boundaries of the form, but they exist primarily as one-offs and oddities. Sometimes this is because the alternate solutions were not very good (remember adventures coming packed with sound effect CDs?) but more often it's because it's a lot simpler to stick to a template, and none of the deviations from the template were such great commercial successes to demand change. And, of course, some of the adventures in this classic format have been genuinely good. Even more of them have been made good through the talents of committed DMs and excited players and that muddies the waters a little.
The point at the end of this is simple: do not feel bound by the structure of traditional adventures as you create your own. Look at your own notes and preparation and consider whether you could make an adventure that looks more those. Look at the things you need to copy or mark up in an adventure and ask yourself why they're not right there in the module. Make the adventure that would be useful at your table today, not at a table in Wisconsin in 1979.
To that end, here are a few points to think about.
Kill Boxed Text - seriously. This is a terrible legacy of the days when it was critically important to mention that there were exactly 7 torches on the eastern wall. Every time I think we're past this particular chestnut, it springs up somewhere else. Instead, consider using that wordspace for something that's actually useful to the GM's and the players. Use it to frame the encounter as a scene, giving the GM an idea of how it's expected things will unfold, and ways it will probably go wrong. This might take the form of tactical advice, or it might be a description to the GM that is actually interesting enough that he doesn't need boxed text.
That's the real kicker of course. Things which actually grab the GM and player attention don't need boxed text. Boxed text is a way to convey the boring stuff. And you gotta ask: if it's boring, do you really need it in your game?
Take Advantage of The Format - If your PDF adventure looks like a book that hasn't been printed, you've wasted an opportunity. You aren't bound by the need to make a specific page count or to conserve whitespace. Consider that a PDF lets you do something as simple as put each encounter on its own page so the GM can easily reference them at the table. That's HUGELY more convenient. In fact, if you assume that people might want to print the useful parts of the PDF, you can go a step further and make sure to include space for notes, tracking damage and anything else. Include handouts because, dammit, if you're printing stuff out anyway, then handouts are AWESOME.
And hell, if you've got the technical chops, make the PDF have a few bells and whistles too. Note sections, checkmark boxes to track monster hit points and power use. This isn't mandatory, but it's certainly a nice bonus.
The challenge, to my mind, is this: can you make your adventure so the GM doesn't need to bring any other paper to the table? Can he print out what he needs, use it for notation, and be done? Consider all the things that you, as a GM, keep track of during an adventure, and what that would suggest. It's daunting, but amazing once you realize it's doable.
Play With Structure - Dungeons are great, but they're only one way to make for good adventures. Look at things like rich locations (Hammerfast), Flowcharts (White Wolf's SAS, 3e's SPeaker in dreams), Hard & Soft Points (Alderac's 7th Sea/L5R adventures), Plot Points (Savage Worlds), Three Fight Scenes (Feng Shui) and many more for ideas of ways to present information. And this leads into the next point:
Steal Good Ideas - Read adventures from games you don't play. It's an amazingly informative thing to do, because in the absence of an understanding of mechanics, the heart of the adventure is laid bear, and sometimes wonderful and sometimes it's just embarrassing to see. There have been a lot of good ideas in adventure design in a lot of different places, but not many of them have trickled back up to D&D adventure design. This is an opportunity for you. Companies may trademarks terms (Pinnacle has apparently trademarked "Plot Point Adventures") but the general method of presentation can be reused freely, just call it something else.
Repurpose Existing Tools - There are certain classic elements to an adventure like the overland map, the hometown, the random encounter tables and so on that are not bad ideas, they just have been treated badly in the traditional format. Fleshing out any of these elements in unexpected ways can bear unexpected use.
Consider Usage - How many good fight scenes can you get in over the course of one session? Me, if I want them to be really good and compelling, we're talking 2, maybe 3 in one sitting. Certainly I can squeeze in more if they're just gimmicky little fights, but I don't like even bothering with those. Plus, if the non-fight stuff is actually going to be interesting, that chews up time too. So with that in mind, how much use do you think a 47 room dungeon is to me? Deferred reward is nice to a point, but something like that is going to take me weeks to go through, and I promise you that in several weeks, my players expect a LOT more. If one of my games were to go 6 weeks without some sort of major turn, I'd have a mutiny on my hands. 6 weeks in a dungeon? Hell no.
Now, that's just me. Maybe you go through fights more quickly. Maybe you're more comfortable with small, fast fights rather than big setpieces. it doesn't matter. What does matter is that people actually need to play this adventure, and that's going to take time. With that in mind, consider each encounter: is this awesome enough to merit me spending my time on, or is it just a speedbump between me and the good stuff? There's a completist urge to put a monster in every room, to make the player fight every inch of the way to the end, and that's got its place, but I don't need to pay you money for a mediocre, time-chewing experience. If it's not going to make the adventure more awesome, just skip it, no matter how much you feel it "needs" to be there.
1 - I'm couching this primarily in 4e terms because it's easier than speaking generally, but a lot of this will apply to any other game as well. Some things are different - I'd be very leery of publishing adventures for a non-open game system, for example, because of IP issues - but the broad strokes are the same. Plus, there's a nice law of inverses at work - other games have smaller markets, yes, but they also tend to be proportionally hungrier for adventures.
2- And if it does come up, it may just take the form of an infodump from an old sage or the like. That is not a meaningful improvement over "never coming up".
3 - If not, the old school renaissance is probably more up your alley. Totally cool if so, but that's not something I can offer much insight on.
4 - That said, man, I am hoping that 4e's new Adventure Site model sells well. Most interesting shift in published adventures since White Wolf's SAS.
5 - When I was running exalted (a white wolf system that uses lots of d10s) i did all my prep on special paper that I'd prepared by printing in advance. I created a left hand sidebar that was 10 characters wide and filled it with random numbers. Since exalted required a lot of die rolling, I used the paper to save myself headaches - if I needed to roll 5 dice, i could just cross off the next 5 numbers and use those as rolls. Something like this for 4e would be a little trickier, but still totally doable.
6 - To this day, I think that X1: The Isle of Dread, is one of the most brilliant adventures of all time, which is absolutely GUTTED by the necessities of presentation.
7 - And going through it will reveal that it's 10% awesome and 90% filler. I'd rather have a 4 room dungeon that's 100% awesome and be done in 1 or two session, simple as that.