I thought it was a good idea to join the various social networking sites, so about twelve months ago I did. I filled out the profile page and listed only some of my published works. There's Facebook, Twitter, JacketFlap, Goodreads, filedby, Shelfari, LibraryThing, and OpenLibrary, and probably a couple I can't remember. Problem I found is that even with "minor" participation I wound up spending far too much time on them. So I limited my participation to Facebook, Twitter, and JacketFlap, but even that takes up too much time. I'm still there and check in occasionally but that's about it. They can be enjoyable, but I think that as a writer there value is way overrated.