There are a lot of variables in play, so I doubt there are many cold hard absolutes that apply. The wiring to a given outlet, the supplied voltage itself, etc., and perhaps most importantly, the power supply included with any given component. I know that Convergent (CAT) goes to extreme lengths with his power supplies, and recommends against any sort of power conditioner. I’m sure there are other components that would benefit from there use, and others that may not.
Sometimes experimentation is the only way to know for sure, but it’s always good to check with the manufacturers if you can.