What made me think of it even more was LibriVox.org, which records common domain books for anyone to download and listen to. I used to work for Distributed Proofreaders for Project Gutenberg for much the same reasons. Uhm, yeah, that's probably where my proofreading skills got pretty good.
Okay, having looked through Distributed Proofreaders again, my brain is like, I could do a couple pages a day, couldn't I? I used to plow through dozens a day after working even. Or hey... that final formatting round looks really good....