At the moment, the Ageia-powered cards are PhysX decelerators. In my opinion, the company have thoroughly embarassed themselves by releasing a consumer-level product that is buggy and actually slows down games.
I'm all for praising them for the initial innovation. Creating a prototype as 'proof of concept' to enhance and accelerate physics in games would have been a good idea.
Releasing it to the public with a sizeable pricetag when it offers very little game support, no 'acceleration' whatsoever (although you could argue that the cards allow more to be displayed than is being portrayed in the 'without PhysX' benchmarks which places more strain on the GPU) is another matter altogether.
Ageia would have been in a much better market position if they had hyped the concept, created some great drivers with existing physics engine acceleration (eg Havok) easily updateable via patch for existing games, and made the thing twice as powerful so that
a) new titles emerge with the card displaying some truly impressive physics rather than 'Is that it?' reactions
b) existing physics-intensive games actually run noticeably faster after patching if you buy a PhysX card
I firmly believe that with some groundwork it would be fairly easy to patch games to place certain physics calculations on their hardware - in exactly the same way that earlier in the stages of 3D graphics cards their were patches that allowed 3D graphics calculations to be passed from the CPU to the GPU.
They could have worked on something more universal, for instance a 'DirectPhysics' layer to make the gap from ingame code -> physX hardware easier for developers and encourage patches for popular existing games - HL2 / CSS would be the most obvious that springs to mind.
Even a proprietary solution would have been successful if it was proven to work well and be easy for developers to use - anyone remember all the games that came out supporting Glide when 3DFX ruled the roost?
But no... release it slow, buggy, and poorly supported, so that by the time the card and drivers are within an inch of doing their original intended purpose in games, the PhysX card as we know it is completely redundant. Either 'revamped' by Ageia or swamped by newly-developed Physics calculation support incorporated into GPU solutions from nVidia or ATI (as has been discussed already).