Ok...still beats me why AMD doesn't allow third-party thermal grease on their products.
Two reasons (and I know this has become a touchy subject)
1) There are some really crappy thermal greases out there.
2) The contact area between the CPU and heatsink is very small on AMD chips, and it's not a truly flat area (AMD's heat islands are very slightly domed).
3) The mounting assembly of heatsink and CPU is not especially rigid and the heatsink can move ontop the CPU rather easily.
Putting these together you get a situation where the grease can actually be pumped out of the thermal junction, leaving you with insufficient thermal conductivity which could (and does) damage the CPU.
AMD's answer to the increasing awareness of this problem seems to be to simply void the warranty instead of improving their products.
---><font color=green>It ain't better if it don't work</font color=green><---