Harry's GPS LapTimer Pro for iPhone
Anyone else use it? I used it this weekend over at Buttonwillow, using only the built-in internal 3G-based GPS (no TomTom or Garmin or Magellan GPS attachments) and despite that, my lap times were only off by 0.1 (compared it against the timing I purchased). Not bad for an iPhone application. Wondering if anyone else uses it with a GPS attachment, and how much more accurate it is.