I'm just going to throw out my 2cents, but I do see how there could be a difference(as with cables and other accessories as well)
BUT... I believe it's due to fixing a problem that shouldn't be there.
ie, buying monster cables might help... if you're replacing faulty, or insufficient cables
and buying a power conditioner may help, if your electrical system is not functioning properly.
if you are getting a consistent and clean electrical signal from the wall, obviously a line conditioner isn't going to change performance. and I'm sure most of us have functioning electrical systems in our homes.
so, as long as there's no problems, these devices don't do anything for performance. and if there is a problem, you're better off fixing the problem then using this to hide it
Displays: Samsung PN64F8500/JVC X35
AVR: Pioneer VSX-1130K, 7.1/5.1.2 audio
Sources: HTPC, PS3, XBOX360, Wii
Control: Harmony One