On: Live from Apple's iPad 2 event

[culturestate]

They use the accelerometer.

[dazmax → culturestate]

I wonder if it has to be on your lap or some surface that has some give for the accelerometer to properly pick up how hard you tap.

[culturestate → dazmax]

I think for maximum accuracy (or at least, as accurate as you can be using this method - I can't wait to try it out), you're probably correct.