If you are interested in predictive lap timing you might also look at "CMS Lap Timer Pro" for the iPhone
But there's a general problem with iPhone GPS based lap timing:
a) the built in GPS of the iPhone is not very strong
b) the iPhone only samples GPS data with 1 Hz = 1 sample per second = if you go 100 mph you have a sample every 150 feet, which is not accurate enough
For a) you can get the TomTom iPhone mount for the iPhone (can be found on eBay) which has a built in much stronger GPS receiver and for example Harry's Lap timer recommends it, but even with it I had "shaky" results with Harry's lap timer
and it seems that for b) some applications support external GPS devices with 5 Hz sampling rates (which is sufficient for racing)
I myself am using a self made rig which is based on PocketPC based software, which is no longer available and when it finally bites the dust I think I'll go with the AIM Solo
P.S.: The only reason why you could think I am Randy Probst is that I am wearing the same geeky glasses as he
