nVidia can impose SSAO on a game via a driver setting. It looks good, although I'm not entirely convinced it's kosher to go back in and modify a game's look that way without involving the developers.
I must admit that SSAO provides visible improvement in some of the examples they've posted. If a driver provides anti-aliasing or texture filtering, that's legit; those definitely provide a qualitative improvement to an image. SSAO however invokes an aesthetic modification on the game. I imagine that I would appreciate it in the case that a game was not strongly art directed, but if a game had a strong aesthetic sense, this seems like maybe not such a good thing. What do you think?