Peter Norvig, Google’s Director of Search Quality, was quoted  as saying at the Web 2.0 conference  last week that Google is using the largest database of clustering in the world. Norvig also went on to say that:
the problem with web search is that an entered keyword could be associated with different meanings, but the results displayed may not be the meaning you want. This is why Google is working on the largest bayesian database of clusters to determine the most likely meaning for any given search request.
Read Andy Beal’s account of Norvig’s exclusive demonstration of Google’s clustering technology  at Web 2.0.