http://www.librarything.com/

I think this will be very useful for the avid reader or libarries but would not use it myself for my reading preferences and discussions, but then again I wouldn't join a book club.

Delicious

http://www.delicious.com/Bossy.bossy
Interesting libarry use.  I like the way you can access your bookmarks from any PC

RSS feeds

I find this very useful for keeping track of SLWA happenings and libarries of interest, e.g. Seattle and Cockburn.  It saves a lot of effort but you d have to quckly delete the junk.