I got to ride with one when my LBS guy let me ride his bike. 'Way too pricey to be worth it for my riding, but oh, my, FUN.
Of course, since I was riding a strange bike - I don't even ride a road bike, much less somebody else's sleek carbon fiber jet - I didn't push much. My average power was something laughable like 75 watts... except that this powertap seems to not do averages right for the speed, so that may also have been off. (It records teh right time, and while we're riding, the speed is the same as everybody else's - but the "average speed" is 'way off, like 10%.)