I have done some extensive testing of my iPhone 4S compared to my iPhone 4 and found GPS accuracy has suffered substantially.
I've been using the 4 for about a year, riding a bicycle on a 3 mile loop park road several times a week. Typically, I'll do about 6 laps or 18 miles. Using a great app called Cyclemeter, I save the track so I have a record of how fast and how far I rode. After I upgraded to the 4S I found the measured length of each lap varied widely and that ridiculously high speeds were being recorded.
Upon examination of the recorded track I find loops drawn out to points up to 100 feet from the actual course and back tracks heading the wrong direction. The net result is the iPhone 4S is off by around 20% on the measured distance from what I know it should be. Has anyone else looked carefully at their tracks and found similar results?
What is more likely: That I have a defective unit OR that Apple's elimination of a dedicated GPS chip means less accurate information?