Although AMD has already earned a good rep for producing cool-running CPUs, slightly at Intel's expense because of the ridiculously hot Prescott core, there's still room for improvement. With Conroe now available, Intel has pushed the envelope for what we expect a chip to do per watt. AMD's answer to that is the release of some very low power dual core Athlon64s. A 3800+ that only consumes 35 watts? That's right.
Not yet available for full retail, it's hard to say much with authority on these chips other than it looks good. The reviews posted are interesting, though I'd like to see how they fare when they hit the real world.