Once Nvidia finally starts pushing PhysX in 2009 and new games, such as Mirrror's Edge and a few other titles that might matter appear on the market, ATI might have a big issue, as it does not support PhysX.
At this point PhysX is purely a marketing thing, as there is not a single important game that supports it and Unreal Tournament 3, the only big title to support PhysX it is not exactly a cutting edge game these days, either.
EA is making Mirror's Edge for quite some time and we were told that this new game that will really push PhysX, will come in 2009, probably in January time, and this might give PhysX a big boost.
In the long run, ATI is in trouble as it doesn’t support PhysX, and this is simply the way where Nvidia will push the 3D gaming market. Games with PhysX do look better, but they have still to appear. We expect more of these games in Q1 2009 and probably PhysX will matter big time by Xmas 2009.
As of Q1 2009, ATI will have to cope with the fact that PhysX-enabled games will run many times faster on Nvidia hardware and ATI will have to find a remedy for it. The only remedy we can think of is signing up for CUDA and embracing its competitors' PhysX that will likely run a bit slower on ATI Radeon cards.
Update: Nvidia also informed us that there is a game called Cryostasis that should show you what PhysX is made from and if you are interested you can download and try some of the games here.You will need a Geforce 8 or 9 series card to give it a try.