Not about racks specifically, but similar.
Our favorite Subjectivist website, The Absolute Sound, was going on again about the minutiae of these new footers and how they changed the sound when placed under his amps and such.
The new part was this:
"Lavrencik believes that it takes about a week for his footers to settle in and that some initial deterioration in sound may be experienced when they are inserted into a system."
http://www.theabsolutesound.com/articles/critical-mass-systems-center-stage2-isolation-footers/
Yes, we are now being told there is a break-in period for footers! And just in case you are not immediately impressed, it may actually sound worse at first he warns, so give it time. The reviewer goes on, spewing descriptive audio verbiage on how it specifically changed the sound for him.
All this can be yours, for the low price of only $240 each and up, sold in sets of four.