At first, it seemed that the GPS was pretty much useless. I tried it from several locations -- inside, outside -- around the silicon valley. It would take minutes to get a fix, if it could get one at all. Now, it can get a fix within a few seconds. So, I can think of three likely explanations.

1. my N900 magically "healed" itself

2. T-mobile fixed something so that A-GPS is now working

3. There's some bug in the GPS software, e.g. some weird thread issue which prevents the GPS from working properly while the device is downloading maps or it's building some kind of hints database for getting a course location fixes.

I'm leaning toward #3 myself. All I can suggest is leaving OVI maps, or better yet the desktop "location" widget, enabled in the background for a couple days and see if your unit doesn't magically start working as it should. ( a few seconds for a course fix, and about 10-30 for a fine fix )