I face the same problem as George. The sensor is always eating up my distance. I had an adaptor on my NB and Mizuno. It's still off even after calibration. But it is better than nothing since I have no other devices .
It is not very accurate but it is good for general record.
I think it is a motivation for running, since it keeps telling you your pace, time and distance, and you can upload to show your friends.
To change the sensor is just $150 ja~