Nice catch spotted via Threadwatch, Google's Testing New Dictionary Feature at Justilien.com has news and a screenshot of Google testing a new dictionary feature that corrects your spelling within the search box. But c'mon already, Google. As I wrote before, if you're going to test things, tell us!
I mean, we can assume this is something you are doing -- but what if it's some program that Justilien Gaspard didn't know he had installed doing this? That's not likely the case, but save us another round of everyone wondering what you're doing until eventually some official word gets out on Matt's blog or via GoogleGuy having to confirm things in a search forum, as we've had before.
You've got a blog -- tell us these things though it. Or start a new Google UI blog that those who care can watch.
Postscript: Turns out this is a function of the Google Toolbar.