All announcements merged thread:
They're talking about 8 GPU machines, 20~40TFlops, because Mantle enable them to implement their own alternate frame rendering.
They were just talking about using the GPU to optimize the work load for the GPU "GPU helping the GPU", they are saying that when destroying a building there is a lot of redundant geometry, and GPU compute can optimize that before rendering.\
"Really big improvement for Windows 7 & 8", "PS4 API shares many concepts and methods and optimization methods with Mantle"
Opportunity for Mantle in Mobile GPUs can "leapfrog DX and OGL"\
"Mantle not tied to GCN, intersting for other vendors as well, can be supported on most modern GPUs"
"Mantle is closer to PS4 than DX11"
"Targeting late Dec release"
"Plant vs Zombies will support Mantle out of the box."