A mining pool by and for fans of the XKCD webcomic and its forum community. Randall Munroe, creator of XKCD does participate.
The proceeds earned from shares are earned by the participants though it has not yet been determined whether or not a portion of the proceeds will be retained to support XKCD.
The service was opened on April 11th, 2011. A web presence for the pool has not been established.
Instructions for joining the pool are available from the pool's IRC channel, #xkcd-bitcoin on irc.foonetic.net