Works great on iPhone 4.0

Im also not sure why there are all these negative reviews. I just downloaded and installed it on my iPhone 4.0 and tested it on my train commute to work. The speedometer, odometer & compass work just fine.

Keep in mind that any app that uses GPS to determine speed isnt going to be 100% accurate, but this is pretty close...and free.

Bazza H about GPS Speed, v1.5