I'll throw my two cents in this "PDF against the world discussion":
When I first bought my Sony reader, I had a bunch of books in various formats I wanted to transfer. I used inDesign to do the work: I created a page template based on the Sony's screen, and laid out the text, including nice chapter titles, lettrines and so on. To this day, these ebooks are the best I possess in terms of typographical quality. Great, hourray for PDF.
But then of course, what would happen if I switched from my PRS-505 to the soon to come PRS-300? How would my books fare when moved from a 6" screen to a 5" one? Or what if I move to a Kindle DX? Sure, my books would still look fine, not a coma out of place, but I don't think they would be very enjoyable to read. Come on, just imagine if editors published paperbacks that were just downsized versions of hardbacks... Would you enjoy reading tiny print text???
So yes, PDF is a printing format. Sure, you can display it on various computer screens' sizes, but the doc only specifies what it looks like on a set page size, and THERE IS NOTHING YOU CAN DO ABOUT THAT. So, if you want comfort, you'll zoom in or out to read it. The only way for PDFs to be a proper option for ebooks is if they were published in various versions that fit your reader's screen size, each edited for that screen size, pretty much the same way and paperbacks are edited separatly to fit. Well, and here come the two cents: "thanks, but no, thank you".