I just purchased a used power conditioner through Audiogon. My observations are simple. It has made a difference in a couple of ways immediately. Since my HT is in my basement all of the electrical comes into the panel located in the same room as the HT. While I set up the theater with its own breakers for the equipment and a separate one for the overhead projector I still had an audible hiss from the amp when idling. Once I made the change over the hiss is definitely gone. I guess that means something but, most notably, I periodically heard some small 'pops and cracks' during both music and movies... that is now gone.
My primary reason though is that we have frequent power outages in my neighborhood. That being the case I have to believe that we also have voltage fluctuations which I presumed could harm the equipment. I believe that this is now remedied.
My reason for buying the APC S20 is that I got it for the same money as a new s15 and I liked the idea of a battery backup.
It is really heavy as the battery is about 50 lbs.
The continuous test feature has shown that I do have pretty heavy voltage fluctuations and while it hasn't tripped the battery yet I will be contacting ComEd for comment. If the fluctuations are not within 'norm' the rest of the home appliances may be at some risk and maybe this is not my problem but something I can put at the feet of the good folks at ComEd. We do seem to have frequent repair issues with all of our appliances......we'll see I guess.