Well since Jude is hopefully busy working on the head-fi store, let me take a crack at it.
I use a custom base of oak and sorbothane under my line conditioners. Why, because they have transformers in them that vibrate. I also damp the cabinets to reduce resonant hum. As far as power amps, you should see the size of the toroidal transformers in my Adcom GFA-565's. They do not vibrate very much because they weigh 45+ lbs, but I have each one on 4 vibrapods that sit on top of a home built oak stand with spikes to couple it to the floor. After I installed the vibrapods I do not feel any microvibrations in the chassis of the amps. However, I cannot claim any significant sonic effect. As far as my preamp, well its is on vibrapods because it is on the same rack as the tuner, CD, and turntable so I want it isolated vibrationally from them and vice-versa. I am a big proponent of both physical and electrical isolation of components.