Have to be honest, torrents. But I'm just trying to build my in print collection as digital. There is no way I'd pay for my 1500+ book collection a 2nd time. Fair use, right?
I have never had problems buying books and I will continue to do so once I buy a reader. Where from? Depends on which reader I choose. Thinking very hard on a Nook or a Sony prs-600. Then again both companies will have something new out very soon :P