I have thought about adding a 3-axis accelerometer to the SD Datalogger for quite awhile now.  I have recently received a set of 3 prototype boards from Laen to do some testing on this concept.  Overall things seem to be working very well.  I am now considering adding the ability to do AHRS in addition.  The question is whether to do this on board using accels, gyros, and a magnetometer or to use a OSH IMU board like the ARDU-IMU.