Do you have a task killer installed or anything like that? How does your phone perform overall? It seems weird that it would skip around like that and your friends doesn't.
When you go into settings > location & security you will see a setting called VZW location services. A-GPS uses the carrier network antennas to formulate an approximate your location using a method called triangulation. The Standalone GPS services setting turn on the actual GPS receiver that uses the birds up in the sky to determine a more exact location. If your satellite icon is blinking, it has not locked onto a satellite yet. You may have already known all that, but I thought I'd throw it in anyways