I played with the GPS using the built-in BlackBerry Maps application last night on my bus ride home.
Overall, I was pretty impressed with the accuracy and speed. The screen seemed to refresh at least a couple times per second and also estimated the speed at which I was traveling.
For the guy asking about walking around in a big city, I live in downtown Toronto -- after I got off the subway I walked the remaining two blocks home and it followed me quite well as I walked. At one point it had acquired 10 satellites, so signal wasn't any issue.
This is my first time playing with any GPS application so I don't really have anything to compare it to but I thought it was pretty cool.