Here's the issue that I have with the shims. Heat from the core does not act like a heat seeking missile and head for the path of least thermal resistance. As pointed out in other threads, quite well by John Car, MikeW and others, multiple thermal pathways are present. 
The primary pathway is between the cpu die and the heatsink, via the thermal copound. A secondary pathway, which actually passes a substantial amount of heat, exists between the cpu die and the ceramic substrate. AMD didn't pick ceramic just for fun. The high heat output of TBIRDS pretty much demanded it. Now we come and cover the ceramic with a copper shim, which touches or comes close to touching the hsf, the primary thermal path. The air gap between the hsf and the ceramic substrate is gone, and new thermal paths are created. Its entirely probable that heat from the hsf heats up the copper shim, instead of the heat in the hsf being dissipated to the air.
As to the idea thats its cheap insurance, considering that you have to remove the foam pads to install the shim, this cheap insurance voids your warranty, both Retail and OEM. 
I am not trying to stop anybody making a buck or two, but there is more to the issue than simply punching out copper shims.