I was talking about the things I was reading here for some time (character-controller, vehicle-functions) and about these two things there are a lot of postings in this forum, just do a search and you should find some infos about it! I actually never used them, but maybe in the future?
The things that people have seen as a problem with DP-particles and cloth are the following:
Particles can't be turned off and on in an easy way (it is just possible to try to use the emitter-rate, but it results in particles just spawning now and then or not immediatlely, when you want them to show)! Also it is possible to delete an eitter, but you would delete also all active particles (looks ugly, if smoke or whatever disappears from one second to the other)! (I tried it and found no satisfying way to turn them on and off, maybe I have overseen something?

)
The thing with the cloth is that you can only create them, but you can't delete a cloth-object once it is created! (This would be helpfull, if you want to reset a scene, where you used a destrucable/tearable cloth-object or when the object get's stuck (it happens sometimes within my "PhysiX-Brick-Breakout"-Game)!)
Also the size of a cloth-object is restricted to 11*11 and scaling results in false positions (I might be wrong with this, but I'm pritty sure)! Some features like the "make cloth from object"-command is not included although it is shown inside the documentation!
Also have a look at the "Upgrade"-Thread, there are some things posted (also some previews about solved problems)!:
http://forum.thegamecreators.com/?m=forum_view&t=101926&b=30
More problems are named in the "EULA"-Thread!:
http://forum.thegamecreators.com/?m=forum_view&t=92726&b=30
At the end I have a link for some more infos about the AGEIA-SDK and the hardware, supported games, tests, interviews, videos,...:
http://personal.inet.fi/atk/kjh2348fs/ageia_physx.html
I hope that helps so far!
Hoozer