Looks like the guys at Google are messing around again with new features. Andy Beal reported that his SEO team has found a "Try Alternate Searches" button at the bottom of the search results on specific computers. I have not seen it myself, but Andy has a screen shot of it at his blog, which I borrowed to show you.
Andy says it does not appear to be spyware, "The link "Try Alternate Searches", when clicked on, takes you to a page that includes other suggest keyword searches, you may want to consider." No official word from Google yet on this topic.
Forum coverage also at WebmasterWorld.