I rented from Jeff the 12th and 15th. I'm hooked. The lateral accellerometers are useless, of course, but the longitudinal ones do provide some interesting data. For a guy like me, being able to see the data really helped me understand how badly some of my habits were hurting me. From one day to the other I gained .3 sec. in T2 and .9 between the entry of the busstop and the exit of T5.
I actually started looking into writing an app to do this with phone hardware, but the speed and accuracy of phone GPS hardware is not up to the task. Not that I expected 40hz, but the 1hz that some of the APIs are limited to is way too low, and my observation with my phone is that it's not going to even do that very well. I may still hack something together as an experiment, but there's a reason a good cell phone is 400 and the traqmate basic is 600, and it ain't all volume.