M3hunter:
I like it. I like the fact that it doesn't affect the warranty (because I had the dealership install it for $70). Maybe you are not concerned about warranty issues (if the vehicle has high miles, for example). The low end torque is much improved, the throttle is crisper (no lag), and the dashpot (engine braking) is much improved.
The disadvantage of the Pro-Cal tune is that it does not have an option for a CAI nor can it been adjusted for a bigger MAF or the Boss intake. If you intend to get the best out of your engine and you are willing to take some risk, you can tune the car yourself with SCT's ProRacer package. I used the PRP on my '98GT and I loved the way the car drove (if I do say so myself, lol).
HTH,
Chris