I couldn't agree more with the comments here. Of all the (IMO) "snake oil" products out there connected to audio improvement, some sort of isolation is really a simple, sensible sound improvement. It's not just made a very audible difference for me with my front three but also cleaned up my sub's response as well. It just took away all the boomy-ness and now I just hear tight clean LFE response. Don't get me wrong, the thing still shakes the house when called for. But I especially notice it in it's musical respose.

Nice to hear that others have noticed a real change too.
I got onto the SuperSpikes because I really liked their appearance under my in-cabinet speakers. They look like simple round feet (I used the self adhesive ones for my L/R fronts) My center has 1/4" threaded feet that allow for tilt so there I used the threaded version.
There are things sitting inside the same cabinet on glass shelves and they don't rattle. And remember my front three all have 8" powered subs in them.