Have you not had the bar before? I've had it for a while, it just used to be blue. It actually goes well with my W7 theme, as my windows are translucent, and desktop background has a black background itself.
Google does have a bad habit of just pushing out changes on their unsuspecting users, without any sort of an opt-in or explanation as to why it would be useful. We all remember the Buzz fiasco. I think they're trying to distance themselves from the Facebook Blue as they launch their new + service.