2 very good topics:
physx and tesselation
The tesselation mode on top-end nvidia cards is rather interesting. AMD isn't without it totally, as there is some option about tesselation in the control panel. However I think it's more specific to certain terrain mapping techniques, whereas the nvidia option is more for nearby model shapes and such. I think the tesselation options will be easily added to AMD cards in the future, or at least the software will do the same work on pre-existing cards.
Physx is a very limited code-set where game coders can program in using this library. It's basically a partical physics type of thing. If the game doesn't code for it from the start, it does not benefit or detract to use either nvidia or AMD cards. When it DOES code for physx, only nvidia cards can run with it, but IMO it's a very minimal thing and game coders can achieve the same result by doing the code/effects themselves, rather than relying on nvidia's hardware. It has to do with glass shattering, things flapping in the wind, etc. None of which AH makes use of.
Here's a quick example of Batman: Arkham City physx on and off:
http://www.youtube.com/watch?v=trq6B4anzjMOf the 2, physx is IMO a marketting gimick and rarely used in games. It's something that doesn't change a game or make a difference. The tesselation looks interesting, though, but IMO it'll be on AMD cards soon enough. It's not something that makes or breaks the game either, as this is usually handled in games with higher-polycount 3D models.