Google now has a new feature: Synonym searching, whereby pages will be found that contain synonyms of the word you enter in the query. Put a tilde (~) before the word in the search, and synonym matching is enabled.
Lively discussion is already beginning about how it works under the covers. Is there a big thesaurus behind it, or is Google somehow tapping into its own gigabase of data to decide on synonyms? From the waxy.org discussion is this tidbit arguing for Google-mining providing the raw data: Bush is a synonym for Gore.