Ageia, whose PhysX card has been unable to acheive any kind of widespread adoption amongst the PC gaming community, has released a free download of their game/tech demo Cellfactor: Revolution. It's a deathmatch-style shooter in which real-time physics are incorporated into the gameplay in a big way. Players can use all sorts of objects in the environment to wreak havoc on their opponents and blow things up in visually spectacular fashion.
Because I'm not generally inclined to throw money down the pooper, I haven't purchased an Ageia PhysX card. When the card was released at an MSRP of $250, its only real claim to fame was that it made some explosions prettier in Ghost Recon: Advanced Warfighter. Now, the card has dropped to $150, and it has exactly this one free game/demo to show off its capabilities. That's it.
The idea of a PCI-e based physics card is not a bad idea (someone had to try), but in this age of multi-core processors and GPU-based physics (nVidia 8800 series cards have physics capabilities), it's just difficult for gamers and develoeprs alike to see the value of adding more hardware. Especially as game engines move toward threading and we see more use of dual and quad-core processors, the need for dedicated physics hardware is questionable at best. This is further compounded by the fact that games do not support physics hardware natively – they have to be coded for it. So while purchasing a new graphics card will give you an immediate improvement to the visuals in all your games and a sound card will provide immediate improvement to audio quality in all your games, a physics card will only provide improvements in games specifically coded to support the hardware.
That said, the card is powerful, and what I've seen in Cellfactor videos is certainly impressive (the game isn't fully playable without the PhysX card). But I have a difficult time imagining Ageia staying in the market for much longer. Cellfactor is pretty cool, and since it's free I highly recommend downloading it. But it's still nowhere near enough to drive a $150 hardware purchase.