Librarything is interesting if a little intimidating. Put in a dozen of my books (the ones I can remember offhand) and found I was the only one who listed about half of them. Can't be the only one in the world who has them... lots of them are old books picked up second hand or republished so somebody out there has them too... I can see using this to keep track of books esp if you loan them out and want to be sure they come back.