Oh, and not being able to copy it among my various machines dooms this too. I do my session notes and creative work on my desktop machine. Then I bring my laptop to the sessions with me... Actually, at this point, pretty much my entire group has a laptop or desktop at the table when we play. So am I going to buy a hardcopy version I can pass around to people as needed, or a software version that I can't? Hmm...
Passing around is possible under DTRPG scheme, as long as you register all the machines under your ID. I've bought BESM d20 Character Journal at home, and then printed it out at work no problem. It works with Windows and OS X, but if you're a Linux user you may be SOL (not sure, never tried it).
I'm not a great fan of books in PDF, so I'd buy any new books I need at my FLGS, but their out-of-print library is excellent and affordable. If I can ever get a Traveller game going, I'll probably buy a few more things from them.