How does it look?
Since PhysX effects are used almost exclusively for eye-candy in Mirror's Edge, it makes sense to go through some before and after images of the GPU-accelerated physics in action. First up is a demonstration of the simulated glass, along with some soft body effects on the window shades:

Without PhysX

With PhysX

Notice that without PhysX, broken glass is no longer persistent, instead replaced by a standard shattering animation. Also, the window shades don't even exist in the game world without PhysX, making the hallway that much less visually appealing. One final item to point out: those little black specks you see in the center of the PhysX image are an example of the simulated debris from ricochets, which is otherwise nonexistent without GPU-accelerated physics enabled.

Next, let's have look at the PhysX cloth effects:

Without PhysX

With PhysX

Many soft bodies simply don't appear in the environment without PhysX enabled, as evidenced by the blue tarp. The tarp deforms and eventually turns into tatters as the helicopter shoots through it to hit the player. In the first image, you can see a pre-cooked puff of debris as a bullet ricochets, while the second image has simulated sparks bouncing around.

Finally, here are the smoke effects Mirror's Edge provides with PhysX:

Without PhysX

With PhysX

Smoke isn't visible all that often in Mirror's Edge, but its rare appearances are generally used to great effect. In this instance, a large amount of mist emanates from the water as the player slides down a waterfall. The whole scene looks a tad bland without PhysX, but the simulated smoke ups the immersion level.

PhysX visual goodness looks best while in motion, however, and screenshots can't tell the whole story. Thankfully, Nvidia provided a demonstration video from a variety of locations within Mirror's Edge, which you'll find embedded below. I've gone to the extra effort of embedding the HD version of the clip, so don't be afraid to click the full screen button. Go on—you know you want to.

The video showcases the full gamut of extra eye candy scattered throughout Mirror's Edge courtesy of PhysX. Pay particular attention to the smoke and cloth effects, because those are both the hardest to represent in still images and the most interesting to watch in action.