Power shifting is where you slam the gas down in 2nd for example, and then when it is time to shift to 3rd you keep the gas hammered and slam the clutch in and shift to 3rd. The second the clutch is disengaged the engine will rev up a bit from you holding the gas down all the way.
I believe powershifting is more like grab/lift/bang and on the gas again. You don't use the clutch at all, just back off the motor for a second while you slam from gear to gear.
I still use the clutch, and shift fast as possible, but I'm not going to ruin my transmission just for a few hundreths of time. My car is not a drag racer anyway. (It is more for fun all-around driving, and it happens to be quick too.) I think most of the Supra's out there are faster say from 30 to 120 than most of the other cars on the road. Some are faster from 30 to 150
BTW, the fastest drag cars are "automatics".