What's the refresh rate/sampling rate for the sudden motion sensor?
The refresh rate of the sudden motion sensor is variable.

The supported bandwith depends on the hardware used; so you have to do some more research on the specific motion sensor used in your model. I've searched ifixit without much success.



According to SeisMac the motion sensor used in the first Macbook Pro is the KXM-52. The specifications state the bandwidth depends on the axis:


  
  x, y axis: 0 to 3000 Hz
  z axis: 0 to 1500 Hz
  


[source: KXM-52 tech specs]

SeisMac itself only allows to set refresh rates between 10-500 Hz in its preferences.