I recorded GPS and G-force data on all laps at the recent Nürburgring trackday. With a little fiddling it's posible to over-lay a graphical presentation of the data. It's all done in the Harry's GPS Laptimer app on the iPhone. The app also does the data aqusition during driving and it is triggered automatically when I go under the Bridge and Gantry GPS points. On Spa it didn't work as convincingly, but I managed to record one lap.