As soon as I order my belt holster from Comp-Tac I'm going to start using my PX4 for USPSA Production. It's a great shooter for me. Even though the frame is polymer, the slide is substantial and provides a very nice balance. The interchangeable backstraps allow you to fit the grip to your hand (I'm currently using the small grip). As Dr. Lunde said, the slim controls make the PX4 a G-model (decocker only) which I prefer.
All in all, I'm very impressed with the PX4 - especially with it's price being in the $400-$450 range. Trijicon is supposed to be coming out with some night sights this winter and there's at least one guy on Beretta Forum making custom fiber optic sights for the PX4.
Jim