*takes off publisher's hat*
Speaking purely as a consumer, I LOVE and ADORE PDFs. Why?
Probably has something to do with the fact that I have a 40 GB external Hard Drive.
There's nothing quite like the ability to pack 500 D&D books (I have about 400 of the old TSR books and another 100 or so PDFs from RPGNow.com) into your backpack (and know that the Hard Drive isn't even a quarter full :b).
Even better that you can search them MUCH more quickly. Also good that you can have an "off-site backup" for free... in case of fire, or what have you. How many of you would be able to replace some of the "antiques" in your RPG collection should the unthinkable happen? I keep a copy of the PDFs that I buy burned on CDs and stored safely in the attic of my father's house.
They're also MUCH easier to peruse/hide at work - especially if you use the "Access" plugin for Acrobat Reader (turns the PDF from "formatted text" into plain text on screen, no graphics, no frills, no columns - much less of a giveaway). ;-b
I have over three bookshelves of RPG material - and let me tell you, at some point, space becomes a cost! ;-)
Not to say I don't have use for printed products... I do. But the format of PDFs is just something I adore. I can copy 'em, paste 'em, and mail them to my DM in advance for approval. I can cut and paste together a file with all my spells - without having to manually type them all in myself.
They have different strengths and weaknesses, but for me, the "coolness" factor of fitting 500 books into my trenchcoat pocket is the biggest selling point for me.
Plus, there are a lot of really nifty ideas out there, and I think it's a shame to miss out on those just because a writer doesn't have enough money to "gamble" (and that is exactly what it turns out to be) on a print run. Especially as it pertains to class books, some of the best stuff out there IMO is only around in PDF.
Of course, YMMV, but that's why I happen to like PDFs as a consumer. I appreciate their strengths and their weaknesses don't matter quite as much to me (maybe it helps that I have access to a color laser printer at work, but I haven't printed a PDF in months).
To recap, strengths of the PDF format you may or may not have thought about:
1.) Much more portable than print books (assuming you have an external HD and/or a laptop) - especially for large numbers of books.
2.) Searches are quick and automated - not like print books ("darn, where was that reference to Malhavoc in the DMG, anyway"?)
3.) Easier to peruse/hide at work.
4.) Easier to backup/replace than print stuff (just burn a CD or download again).
5.) Easier to "copy/paste" stuff from since you don't have to type yourself.
6.) More immune to "gamer crud." Somebody spills Mountain Dew or drops pizza on your print book, you're pissed. Somebody does it to your PDF printout and it's "ah, no problem, I'll just reprint that page." (Drawback: Somebody spills on your laptop and you're REALLY REALLY pissed LOL).
--The Sigil