As much as I love my RPG pdfs, and as convenient and as handy as they've been, there's one area they can't hold a candle to my print RPGs--that "book smell". I've always thought books have the greatest smell about them--walk into a library, and just smell all that paper and print!
New RPGs and old RPGs also seem to have their own distinct smells--new RPGs smell a little sharper, have a bit more of a glue-y smell. On older books, its a little musty, but the paper takes on a scent of more subtle gravity. If they made a Yankee Candle out of it, I'd definitely pick it up.
The room in my old FLGS that had all the used RPGs in it just smelled like gaming, you know? I don't mean geek sweat and Mountain Dew, either. I'm talking about rummaging through your Player's Handbook some late Saturday night, or looking through a bunch of books during character generation for a new RPG.
I don't make a habit of going around and sniffing books, but it is something I've noticed, and I don't think I'm alone. Until there's scratch n' sniff pdfs, deadtree is going to be sticking around.