Emerging from lurking mode for a second to make a few points about Mantle.
Mantle is the direct result of a number of AAA game developers asking us for something like this because of several constraints they're experiencing with existing PC graphics APIs. Those developers want to get closer to the metal and able to achieve more with the GPU(s) on their PC without the API getting in the way of this effort. "More with more" is the term used by Raja and it couldn't be more spot on.
AMD listened to developer feedback and entered this venture with Johan Andersson leading the charge. Johan has a passion for writing efficient code that can allow him to accomplish his technical vision and Mantle exists to serve this purpose.
Mantle is not for every developer. It is a low-level graphics API designed to drive the GPU in the most efficient manner. This level of access requires a bit more development effort than existing APIs to reap the rewards it provides.
AMD remains committed to support DirectX and OpenGL and to keep optimizing our drivers for those APIs. Mantle is an option that some developers may choose, but it does not affect those that wish to keep using existing APIs.
Some technical concerns are mentioned on this thread. The Mantle API has been in design and development for more than 2 years and rest assured we've had some time to think about the best way to address those (and loads of others).
More technical details about Mantle will be revealed in due course. Johan is a keynote speaker at the AMD Developer Summit (11-14 November, San Jose).
Nick - Gaming Engineering Manager, AMD