My most interesting experience with a powerback took place in Asheville, North Carolina on a US Airways flight several years ago. After we had left the gate, the pilot starting taxiing down the wrong (very narrow) taxiway towards a general aviation ramp--- once he realized his error, he stomped on the brakes. After remaining motionless for a couple of minutes--- he "kicked it in reverse" and proceeded to power back all the way back to the ramp, where he then selected the correct taxiway and we continued on to the runway for takeoff.