More experimenting by Google, this time Google Groups results appearing at the bottom of search results pages. More important, it's getting seriously annoying that Google isn't doing any heads up on this stuff. One of Google's strengths was consistency. Things just didn't change around all the time, as with the bad old days of AltaVista and gang. As I wrote before, if they're going to try things, tell us!
Back to that testing, Google Blogoscoped has a screenshot of what was pointed out to them. A few minutes ago on a different search, I saw the same thing -- Google Group results at the bottom of the page for a different query, but I was unable to reproduce that. I'm guessing you might also see other OneBox style results such as Google News or Google Local down there.
FYI, this particular test may have been going on for some time. It's just not a particular implementation I've seen recently or read spotted by others. For more on other tests, see our More Testing Of Middle Of The Page Query Refinement At Google post.