Wow.
I've never been a proponent of muffling of any flavor -- duct tape, zero rings, dead ringers(let's see who's old enough to remember those things! I think they got out of drums and went into the home insulation biz!), etc...
I picked up a batch of this stuff. Blue goo, like reusable Jello. About an inch square per piece.
So far, I've just been messing around with this stuff on snare drums. One little square takes out JUST enough of those unwanted overtones, and gives you a controlled, yet still open and natural sound. Very cool.
The nice thing was that the moongel was very responsive to placement around the head surface. For instance, you can have it on the very edge of the head, with a bit of it draped on the rim, for just a bit of damping. Or, you could put the whole thing about an inch inside the outside diameter for more damping. The choice is yours.
Anyways, check it out. Moongel.
http://www.rtom.com/damperpads.htm