FWIW, here's my take on the matter.
This is not legally binding on my part, but here's how I personally view it.
If you buy a PDF from S.T. Cooley Publishing (my company), you have a license to make as many copies as you need for your own personal use. Specifically, I expect you to have at least two copies on storage media (I won't get into "storing in RAM while it's displayed on screen") - one copy, say, on your home computer's hard disk, and another copy on a CD Archive of your stuff.
Furthermore, I have no problem with you placing a third copy on, say, your PC at work. Or a fourth copy on the laptop you take to games. Or whatever. You know when it's for YOUR personal use and when you're trying to "distribute it around." As long as it's for your own personal use, I don't care how many copies you make. It's none of my business, in fact. I would suggest the same holds true for printed copies. If you want to print one "nice" copy and bind it for your bookshelf and print one low-res, B&W "gaming copy" to mark up, I have no problem with it.
Things get a little trickier with your gaming group. I would say it's easiest to go by a "one printed copy" rule. By this I mean you can "lend" to a friend one printed copy. While he has this copy, you may not lend any further printed copies out. This makes it possible for your DM to review material between sessions (if you're a player) or if you're a DM, it allows your player to decide whether he wants that nifty prestige class. You have a copy for your personal use. Your DM (or player) has a copy to allow him/her to do what is necessary as well. Everyone's happy.
Of course, you'll also note that all of the text in my products is OGC (expect for a few very limited things like my company name, my own name, and product names). This is done deliberately - it means you can distribute it as much as you want, though you'll have to do a cut/paste.
FWIW, in the upcoming Enchiridion of Treasures and Objects d'Art, many of the pictures will be placed into the public domain to allow easy copying (some will not be).
My philosophy is that people, by and large, want to do the right thing. I expect that there will be a few that try to take advantage of things, but most people are more than willing to pay for quality content. I'm not going to put a burden on the vast majority to try and spite the few.
If you like my work, please pay for it. You know it's the right thing to do, and I hardly think the price is exorbitant. But I'm not going to piss off the vast majority of you trying to track down the few people who are passing illegal copies of my work. It's not worth it to me. I do this because I love it, not because I am trying to turn a profit. All of my PDF sales tend to get re-folded into the RPG community at large - I use almost all of the money so made to buy RPG material anyway. It's my "play fund."
I think I've made my point. I could easily say, "Mr. Consumer, you know what's morally right and wrong, legal ambiguity notwithstanding. I trust you to do the right thing. If you don't, it's on your own head." It accomplishes the same thing.
--The Sigil