I don't know about all that... Power can have noise - depending on what you have hooked up on the same system. You can hear faint radio signals while playing CDs on some systems if you play the CD really loud and put your ear very close to the speaker
. Its not night and day - but for people who want to pay more, it is better. The thing I am referring to here is isolation. There are several things that Monster - and other power conditioning systems by other companies, can do. Another is maintaining an even 120 volt power supply even if the power is at 110 or other voltage. Some systems may exhibit slight loss of quality when voltage isn't perfect. There are some audiophiles (few) who run their amps off batteries because of this. I am more into audio than video - don't know exactly what this will do with a plasma (which I would suspect would have fairly good voltage regulation inside it already), but for audio I can tell you for 100% sure that if you have an extremely high quality system you will get #1) a lower noise floor, #2) better isolation of components electrically from eachother, #3) voltage regulation if the particular piece of hardware offers that (not all do), #4) higher Joule protection than most power strips.
If you have a friend who has one, borrow it, plug everything in, see if you notice a difference... Oh - and I don't know if the ones that cost 200 or less will really do anything except some isolation and the higher Joule rating, you've got to spend more than that to really get clean power.
One test - without such a device run your system, plug a vacuum cleaner into the same wall socket, then run the system + vacuum cleaner (or a bank of fluorescent lightbulbs - those introduce tons of noise into electricity) and then do that test again with all your electronics plugged into a power controller thingy. Big difference!
You might say you wouldn't run a vacuum cleaner while watching a DVD, and that is fine - this is just an example that it is really doing something.
Make sure your system has many bucks spent elsewhere first, but if you've got budget for something like this and know from the outset that it will bring marginal improvement, then go for it!
Again - no knowledge of effect on Plasma TVs, but for high-class audio it definitely helps!!!!