Well, here is what i have heard about the GT-S
First off the tranny is ****e. The gears are cut relativly thin to make room for the 6th gear. And becuase of that arent very sturdy. Supposidly with any aditional power adders, the tranny will fall apart from the excess torque. Ive also heard that the diff is preaty weak. And the right (i beleive thats the side with teh longer half shaft) will go out, and loose all power to it. Wow...1 wheel drive FF with no gear box...sounds fun.
The engine is kinda pesky, the VVT-i system is really a pain when working with forced induction. And valve cracking is common under high boost. Also the valves slapping the piston from over retarded timing at low RPM can happen. Head warping can also happen from what ive been told, due to improper managed VVTi under boost, and excess heat builds up.
Now, where i read most of this info was on a Celica enthousiast site, with people complaining abou the TRD clutch damaging their tranny, and how the dealer wouldent replace their tranny anymore becuase its their 5th one etc. So i take this info preaty seriously. If i can find the site again, ill post a link.
I was looking at getting a GT-S a year ago. And after reading that forum, i was completely turned off to buying one.
just my 2¢.