If funky and homemade is your thing, there's always librarything (which also has a real business model, so not likely to get swallowed up any time soon.)
Apparently, Amazon holds a 40% stake in Abebooks which owns LibraryThing. From Pandodaily, "Amazon already owns Shelfari as well as Abebooks, which bought a 40-percent stake in LibraryThing in 2006, so it owns all or part of three of the top social-reading sites."
