Today, I put together a web page topic tool by using the web service that Nathan Davis made available. The tool takes in one or more web pages (i.e., a list of URLs) and then extracts the topics given the text on the web pages. The topics, or more accurately, the most likely topic components are extracted using an algorithm called Latent Dirichlet Allocation (LDA).
One potential use is for quickly generating blogger profiles to be used for implicit affinity networks. You can try it out at:
Nathan uses his web service to make the query expansion service for Google searches called GooEgg.