There is a site where you can go and proofread ebooks destined for Project Gutenberg, where they make available free electronic versions of books that have passed into the public domain (are more than a hundred years old). This is a very good thing.
See, these old books aren’t popular with most people, but they are there, and with a little effort they could always be there, for anyone who could ever need them, ever. Such a database/library can only make us as a culture richer, as well as each individual richer in their options of free material. The problem is that when the books are scanned in they are just photos of pages, which transmit and store poorly, so text-recognition software is used. But the software makes mistakes, sometimes a lot of them.
Thus someone has to go through all the machine-generated text and make sure it’s kosher, that’s where you and Distributed Proofreaders come in. They offer a simple web interface where you can donate a few minutes of your time, one page at a time.
Consider it, Project Gutenberg could be the next library of Alexandria, and you were just going to waste your time anyway.