Ask HN: Algorithm behind Googles Similar search feature

Google recently mentioned the "similar" feature in search on its blog. http://googleblog.blogspot.com/2010/04/discovering-pages-similar-to-ones-that.html

Any one knows what kind of algorithm Google might have used in this feature or any public papers/ patents by Google related to this feature?

My interest in this feature is due to a paper which i wrote (and working on) in International Semantic Web Conference this year [ http://data.semanticweb.org/conference/iswc/2009/paper/poster_demo/130 ] and which is based on a paper by Common Sense Computing group at MIT Media Lab [ http://xnet.media.mit.edu/analogyspace ] .

Akshay Bhat