Same GPS issue
Mine started Friday night. I reside in Chicago and ATT's network has shown me in Akron, OH for 3 days now. There are a couple threads on Nokia support with the same issue, so it seems to be fairly widespread. It also appears that it started for most people this past weekend.
From my experience, it doesn't seem to be a hardware or WP7 issue, but rather an ATT location services issue. It seems that most people who have the problem are being told they are at 249 Firstmerit Circle in Akron. I've spent all morning messing around with it. I cleared the map data and history, turned on wifi, and turned off ATT data and all location-aware apps worked fine. When I turned on ATT data and turned off wifi, it took me right back to Ohio. I also tried removing the SIM and starting wifi, which also fixed the problem until I re-inserted the SIM. Apparently someone did some digging and found an ATT Data Center a couple blocks from the Akron address, so it seems like some kind of default location for aGPS. Regardless of the cause, I hope ATT/Nokia/Microsoft find a fix quickly, because all location-aware apps are now useless.