OK - reason #143 why the iPhone is AMAZING. Now that you can download apps for the iPhone I have found some really cool free ones like the magic 8 ball and the light saber apps. But this one has to take the cake.
The iPhone has an accelerometer built in and besides flipping the screen sideways, it is going to give me a speeding ticket.
For $13 I downloaded "Dynolicious" which (among other things) measures the 0-60 mph times of your car!!! It also uses this data to calculate some other cool things like the horsepower of your car.
I was only able to give this bad boy 2 tests but I have to say I feel the results are quite accurate (or close enough for recreational use). My 0-60 mph times were close to advertised but a little slower since I wasn't doing anything fancy to "launch" my vehicle at the start (revving the engine then dropping the clutch). Consequently my horsepower calculations were also a bit low but above 300 hp. I also believe you have to find a flat stretch of road. I may have been going slightly uphill. It did say that I was pulling 0.80 G's max which is either just instantaneous (since 0-60 I calculated an average of 0.55 G's) or partially due to the fact that I may have been going slightly uphill.
DISCLAIMER: Just as dynolicious says, the software is intended for experienced drivers in suitable locations. You alone are responsible for any accidents, injuries or property damage that may occur. Always drive safely and obey traffic laws.