For those who don't keep up with Project Gutenberg, the Distributed Proofreaders project is currently in the process of proofreading an OCRed version of the 11th edition of the Encyclopedia Britannica.
Anyone interested in helping to proofread for OCR errors can do so at,
http://texts01.archive.org/dp/
(DP allows users to proofread as much or little as they want in increments of single pages).
Incidently if anyone had any Public Domain books (pre-1923 generally) which they wouldn't mind giving up (and aren't already available in Gutenberg) they can post them to the admins of the DP website to process for Gutenberg. (They have a high-speed destructive scanner, but are running low on material as they get through about 4000 pages/day)
Imran