Recently picked up the new copper clad version of the StarrDamp material. First I visually compared it to the Home Depot aluminum roofing tape which has been mentioned before. The sticky material is different on each. Therefore the dampening properties would probably be different. VeraStarr has claimed that their sticky stuff was superior in sound dampening capabilities.
At any rate, I applied the StarrDamp to the back and perimeter of each of my driver's magnetics. I also applied as much as possible to the metal frame which supports the drivers themselves (My main speakers are Hales Signature Two's).This is a rather time consuming process but was well worth it!
I fired up my VTL's, let them cook for an hour and sat down for some critical listening. The immediate impression was a more relaxed, analog sound originating from my Wright Modded Sony 9000ES DVD/CD player. No loss of detail but sooooo smooooth. The bass was tightened up a bit also. This tweak in my system turned out to be fairly significant. At the price of admission, I would definately recommend you give it a try!
I have enough left to treat the Sony which I will do at a future date. Will let you know what the results are.