I have found PFX to provide very useful solutions where other approaches would have been time-consuming or even impossible. Outside the obvious function of making a quick forest or garden if you need one...other things I've used it for is quick rain and snow, tentacles on a jellyfish, intestinal wall cilia, animated graffiti strokes, a walking pencil-sketch man (by attaching a pencil brush to curves on an IK setup),etc.. Also I've used the Canvas mode for quick texturing of objects and watercolor-y backgrounds.
The problem is that you really have to dig into it before you can do anything surprising. The ability to use your own texture maps is really powerful, and the built-in dynamics are super-fast, much more plug and play than the regular Dynamics tools. Painting on objects is a great way to spruce up a landscape scene.
Lots of uses. have fun..