If you like to classify your books: Goodreads. It’s LibraryThing, version social network, and with a nicer design (via Michel). Like it.
odesk: for freelancers to find contracts worldwide. I think I’ve seen other versions of this, but this application seems quite mature. I’d like to hear some customer opinions.
enlightening post about how to use someone’s browser history to customize his/her experience. Smart, but my instinctive response to this is Preferences -> Privacy -> always clear my private data when I close Firefox.