From what I understand... they are BULLSHIT! Kinda like Monster Cable... However they do provide you some added protection in case of a indirect lightning strike. (A direct strike will Melt your Receiver/TV/AMP to the floor... hehe)
The reason is that your Amp and Power supplies probably use big compacitors on the output of the board. They are designed for the irregular power from the company.
Yet, If you have cheap equipment they probably make allot more of a difference then the big AMPS!
I havent seen any research on the topic, but it would be difficult, cause it would be based on your individual system.
So if you want... buy it, and try it out... do a REAL double blind study... and if it dont work, return it.
As far as money spent... I always push for speakers as the number 1 area that you should spend money on. Then Amp/AV Receiver... Then lastly Cables and these accessories.
WIth all this said, I was thinking of running it between my UPS and my Computer. I find my UPS will swing 5v and some Hz on the AC channel... makes me worry... I can watch the power from the wall, right from my computer... of course it is just a snap shot, or a average... and it may not be adequate.