On the Peach blog, Brecht introduced a new method of Ambient Occlusion called Approximate Ambient Occlusion. At the time of the post it was not available in the SVN, so in turn not available for use by the masses. But that has changed you can now find builds on graphicall.
More information is also available at Blender.org. And a thread at Blenderartists is open to discuss the feature.
Again see graphicall for builds with the Approximate Ambient Occlusion.
