Me I tend to use the pdf as a way to experiment, b/c I love the asthetics of a well done book, esp something like Ptolus
I will be picking up the Spirit of the Century/Don't Rest Your Head combo for $20 (and adding Spirit of the Season b/c it looks like it will be ridiculously fun to at least read). I've heard nothing but good about SotC and DRYH just sounded insane in all the good ways I haven't gotten to experience too much since the dyas of playing CoC in college heh. Ken Hite's encapsuled review of it is selling it enough on its own.
“Makes the Call of Cthulhu sanity death spiral look like a handful of baby asprin.”
“… it plays like Call of Cthulhu on crystal meth… This game is really well done, no matter what your dreams are like. And if, like mine, they come from a rich diet of Grant Morrison and H.P. Lovecraft, then this game will tear open your skull and let the monsters in.”
— Ken Hite, author of Nightmares of Mine
Not trying to threadjack, just giving an example of the power of pdf for me. If I enjoy the books a lot I'll pick up print copies someday.

“Makes the Call of Cthulhu sanity death spiral look like a handful of baby asprin.”
“… it plays like Call of Cthulhu on crystal meth… This game is really well done, no matter what your dreams are like. And if, like mine, they come from a rich diet of Grant Morrison and H.P. Lovecraft, then this game will tear open your skull and let the monsters in.”
— Ken Hite, author of Nightmares of Mine
Not trying to threadjack, just giving an example of the power of pdf for me. If I enjoy the books a lot I'll pick up print copies someday.