How will WotC stop me? In the end, if anything else fails, I can just write it down with pen&paper right from the screen.
Isn't as much work as it sounds, as I usually only use very small part of a supplement anyway (e.g. from Complete Warrior and Complete Adventurer I bought for my rogue/fighter I am only using one PrC from Complete Adventurer and one feat from Complete Warrior,w ith the rest of the books having nothing that interest me.).
So even if WotC blocks downloading, direct printing, copy&paste printing and even screenshots, in the end they can't block my own hands using mere pen&paper to get the 12 powers and 4 (magic) items (high guess) I want from a particular supplement.
If I want to make me "power cards" for easier management of my encounter/daily powers I would have to write it all down anyway even if I bought the book.
If I go to a convention I also never carry any books with me anyway (saving weight, preventing loss and damage), I just have a folder with a copy of the few pages with the rules concerning my characters for the Con.
I guess I will still buy a PHB, but anything else? I don't think so If I can browse through all new books and cherry pick what I want from them for just $30 a year