I'm already on LibraryThing, but Good Reads looks like an interesting site too. I wonder which will come out on top?
Edit. Just thought I'd add this. It's a Technorati search on all the people kind enough to join Hal Spacejock's Support Crew:
hal spacejock support crew
Simon Haynes is the author of the Hal Spacejock and Hal Junior series (Amazon / Smashwords / other formats)