I've developed a Screen Space Ambient Occlusion plugin for Shake that I'm releasing for free (as all of my other plugins). It's using only a depth pass to calculate a kind of ambient occlusion pass. First it's calculating a normals pass from the depth pass that is later used for the occlusion sampling. If you got a normals pass already you can feed that into the node as well to get a better result.
The whole plugin is actually a macro that includes 3 compiled plugins:
depth -> normals
depth&normals -> noisy SSAO
noisy SSAO -> smooth SSAO
These ones doesn't show up in the interface as default, but you still have them there to use as you want for other stuff. I can see uses for generating a normals pass from a depth pass, but also being able to blur stuff without blurring the edges of objects or sharp features.
The plugins are downloadable here:
http://www.pixelmania.se/shake
I have optimized it as much as I can for now and it's still slow, sorry about that. It's just loads that needs to be calculated for each pixel.
Hope you like it!
Cheers, David