I'm writing this from an internal window in Buzzbot. A lot of "Internet marketing" stuff (and yes, that's an affiliate signup link), but the concept itself is pretty interesting:
It looks like a GUI desktop. It acts like one, too -- there are games to play, widgets and gadgets for watching YouTube videos or whatever within the screen, etc. I actually found the YouTube window more user-friendly than opening YouTube itself in a normal browser window.
Buzzbot's main "Web 2.0" claim is that it makes every web site a "social networking" site. When you open a site (any site you like) within the in-browser GUI, it opens with chat, comment and blog tabs attached. The theory, I guess, is that eventually there will be enough Buzzbot users flitting around the web that they'll be "meeting" and interacting at these other sites, creating one massive all-encompassing social network.
I'm not ready to drop Haloscan commenting from KN@PPSTER just yet, but the concept is engaging and I plan to play around with it some more. As far as the "Internet marketing" angle goes, I don't have a handle on that yet, so I'm not going to try to sell you on anything other than perhaps giving Buzzbot itself a test drive (the parts of it I've described are free).