I recently received a pair of Purons to try out on my main stereo. I honestly was not expecting to hear a difference as I'm using a full Puritan system (PSM156, Ultimate power cord, GroundMaster, RouteMater, 10AWG dedicated line, Environmental Potentials EP2050EE & EP2750 at the panel, WireWorld Silver Electra 7 power cords from the Puritan to all the gear). I plugged one into the duplex and the other into the Puritan (position closest to the power cord) just before we left town for a couple of weeks.
I've always found it easier to hear differences in sound quality when I remove something from a stereo rather than after putting it in. I listened for a while with the Purons in and then took them out.
I heard a slight decrease in the already very black background and slight collapse of the sound stage. Remarkable considering how highly optimized the AC already was.
I would imagine folks with lesser or very little AC optimization would get an even larger improvement. I consider the Purons to be one of the better values in high end audio.