Vivisimo launches it's own SE or "clustering engine", clusty.com see http://stuff.techwhack.com/archives/2004/10/03/vivisimo-clusty/ I think it's an interesting concept. But i'm not sure how their clusters are generated and where my sites are.
There are very smart folks behind the parent company, do some research on Vivisimo and you will find that out. They will be a major player in search.