Mine started doing this too, but it started a month or two ago at least. When I reboot or even take the battery out and reboot, it would usually be ok for a very short while when it would come back up, but then start freaking out again. It would always go back to normal if I would leave it alone for say 10 or 15 minutes.
One thing I'm currently trying (I only did this 3 or 4 days ago) is I had had the weatherbug big widget on my home, and over the weekend I removed it (did not uninstall weatherbug though). It has not happened since I removed it, but, since it's only been a few days, that's not conclusive yet. It seemed like it would happen maybe once a day or every 2 or 3 days. The first time it does it now though will prove weatherbug isn't the cause.
Anyone else experiencing this and using the weatherbug 1x2 widget?
Also: I only see this whlie the phone is unplugged, but I always unplug it to use it. I only use the charger that came with it.
Update: The issue occurred again with the Weatherbug widget gone, so it would seem that's not the cause.