The question do power conditioners help or hurt can't really be answered with a simple yes or no. Some help, other hurt, others don't do anything. In general the cheap stuff is nearly worthless. Surge/spike "protection" is provided via noisy, sound degrading sacrificial MOVs that are ineffective at stopping most kinds of power problems. The cheap power strips also almost always use a type of power filter that severely limits current, which is why you will see dedicated "high current" or "amplifier" outlets with less filtering - avoid.
Once you get past the junky Monster Cable stuff, companies attempt to deal with AC line noise in a large number of different ways. Active regeneration is not the holy grail that companies like Exact Power, PS Audio, or PurePower make it out to be. I've heard a few of these, both the old linear amp based heat monsters, and the new efficient digital amp variety, and while good, I don't think they are in the same league as the best passive conditioners.
Balanced transformers are probably one of the oldest types of conditioners, but the best models from B-P-T and Silver Circle can still sound fantastic. The downside is that a big enough transformer for a full system is going to be heavy, and there's a possibility of annoying transformer hum.
Capacitor based conditioners can also be superb, and they don't have the weight problem of a big transformer. No hum either. IMO the Audience Teflon conditioners are the best of this type. There are also inductor/capacitor based models, which I think is how the Running Springs and Isotek units work.
Then you have the really out there stuff - Synergistic Powercell, the Audio-Magic black boxes, and the newest Shunyata models which have moved away from capacitors and now just use purely passive noise reduction compounds in big tubes.
