I would like to second every thing Defiant said!
Excellent post, and should be read by everyone before they mod their cars extensively.
I usually drive around town with my boost controller dialed back to near stock boost settings as I simply cannot use the power higher boost levels gives me.
The other issue many new folks fail to comprehend is that the real issue is power to weight ratio. Many of them are thinking of performance levels of cars where 400 whp is in a car that weighs close to 4000 lbs. Add the additional traction of AWD and 300 whp in the Subaru's will match up very well with some of these "higher powered" cars.
Even an experienced driver can scare the crap out of himself with 300 - 350 AWHP. You can have too much power for the street. (been there done that) It is no fun tip toeing around in a car that makes so much power you can never go full throttle, and if you do you have closing rates on other cars that are so high the other drivers have no clue what is happening.
It is a perscription for an accident, if the other driver glances in his rear view mirror and sees you just starting to pass and thinks oh heck I will pull out in front of him and pass to, by the time he completes his lane change and looks again you are going 100 mph and are 15 ft from his rear bumper.