This is new to me: Microsoft Research Asia appears to be working on clustered search results a la Vivisimo. I saw this URL: http://rwsm.directtaps.net/ in my referer log which give search results with the familiar clustered tree on the left.
It looks like this has been around for a while, at least since the end of January.
Update: Ok this is old - but still new to me. Here is a post from July 5th 2005 (!) mentioning the site.