there are 2 sensors, as you know. the one I broke was on the wheel for speed, not the reed switch by the bottom bracket. The plastic sensor that clipped to the plastic holder popped off. This happened on a 40+ mph descent where I was racing another dude (there's a town line at the bottom, and it's all about positioning and tactics). I think I hit a pothole pretty hard and somehow the sensor popped off the plastic clip on my fork. That's all she wrote for that guy.
ps -- i lost the sprint