Besides some other nice features Google Desktop 3 supports searching over multiple computers. To allow that even if another computer is shut down, documents are uploaded to Google's servers. Well, it's obvious that you need that to make that functionality real, but: who would really want to upload his private documents? Have they gone crazy? Or evil (Hint: Google's motto is "Do no evil").
I started to use more and more functionality from Google lately (gmail, desktop2, blogger, ...) but this really frightens me! Maybe i have to rethink my decision!