I guess if you were trying to build an inertial guidance system, they would be useful (if you had something against gps, or couldn't use it for some reason). However, the simple task of detecting the orientation of the handset is easily accomplished with the accelerometer (gravity points down...look for the force vector corresponding to 9.8m/s^2 acceleration and compare to baseline axis orientation to get degrees from vertical)..plus the accelerometer does other things as well (in addition to being immune from the need to be reset/calibrated). For just about every use case I can think of, gps + accelerometer + digital compass trumps the need for a gyroscope set for a non-mission-critical, non-military customer. Since those items have other functions that are useful in their own right...I just can't see the justification for adding the cost of a gyroscope set (3 axes would be an additional $150 plus the added challenge of show-horning them in to an already crowded case).

But that's just me...