
Good old LibraryThing. I initially created an account sometime back so that I could get a visual display in the sidebar of my bookclub's blog. I also had the chance to hear Tim Spaulding, creator of LibraryThing, speak at last summer's ALA Conference. I have not gotten into the community aspect of LT but I'm sure you could make fast friends with someone who had the same book on their shelf.
I do like the tag search that allows me (the searcher) to skim off the wisdom of the people (you). I just combined "humor" and "nobel prize" and came up with this list. Perhaps helpful to someone.