Collaborative search is a great 2.0 conceptual execution. Use the wisdom of the crowd to give more useful search results, prioritized by humans of similar attributes as the searcher. StumbleUpon poorly named but well intentioned player in this space. I gave it a whirl as a potential source of traffic for this site. Sign up was easy, nice site, good colors, lots of kitchy preloaded avatar images. What’s this? Download a toolbar? Something that goes all the way across my screen and contains your logo and writes things to my registry.

Edit: The Firefox Extension implementation of StumbleUpon with hotkey on/off is totally cool and no screen real estate is harmed so I am going to play around with it and see.
Alt+F4. See ya.