I have to jump in and say that while power conditioners DO make a difference, many people won't notice this difference because their music system can't pick up subtle difference to begin with. As a general rule, if you have a system that is under $1000, you likely will not get the benefit with a power conditioner (at $200).
People seem to expect their $500 home theatre in a box would magically sound 10% better, however these people would likely be disappointed. They may feel what they bought is an over glorified surge protector, when in fact it's not. It does work, their system just can't resolve the difference. Also, even with expensive systems, the difference in sound quality may be subtle to the casual listener, but those who are discerning would notice the difference immediately. I'd say sound quality improvements one might expect would be in the 4-5% range.
I recently got a Monster HTS 1000 power conditioner, and was open to anything that might happen. If it didn't work it goes back to the store. Hence I wasn't trying to justify a purchase. Anyways, I did extensive auditioning of several CDs going back and forth several times using the HTS1000 and a regular power strip. The sound quality differences with the Monster is pretty apparent.
My notes on the benefits of plugging my system through the HTS1000 are below.
1) music has more impact.
2) greater see through transparency and detail.
3) more SPACE between instruments (i.e. instruments did not sound mashed together resulting in flat sound as was before)
4) bass is tighter and has more punch
5) hear greater subtlety in vocals, and cleaner sounding
Those who criticise Monster products or power conditioners in general would say I'm just "hearing things." Whatever makes them feel better. I couldn't care less. I'm not promoting this particular product.. but I do have to point out that many people do hear improvements with power conditioners. Certainly this is not mass halucination.
