The Search Engine Guy writes "Google is now using "Stemming" in it's search engine results pages. This will make it easier to get wider and more relevant results for queries. It will not be necessary to add "s" or "ing" etc.This is the latest algorithmic change - the last one was allowing "Synonym" searching with the "`" before word one wanted synonyms for to be included in a search."
It doesn't appear to happen with all searches, but take a look at your results and you might notice. searchengineshowdown.com and searchenginewatch.com have some more info.