I have two iPhone 4. One JB and the other is not. I wanted to test the GPS in Google Maps app. The JB iphone can not pin point where I'm at. It keeps moving around and is no at my exact location. However, the non-JB iPhone 4 is locked to my actual location. No movements. I wish I had another iPhone 4 to post the video. Perhaps I can do that when I get home tonight. You guys should test your iPhone and let me know if you are having the same issues.