i doubt they would have major build quality issues on their GTOs, as i have had my gts for well over a year now and i have put 80 000 km (50 000 miles) and the only gripe i have is that the dash is starting to creak a bit but apart from that the engine is still horny as hell and i the car overall is in pretty tip top shape
I saw on a "another" GTO site that an 04 owner who had his car for a week said the stereo would shut off periodically. He said it acted like the amp would overheat, and auto shut down. After it cooled down, he could power it back on. He also said his rear-window defrost wasn't working.
I only have put 500 miles on my car thus far but I have had no problems. No radio shutting itself of or any other wierd occurances. I have not tested my rear window defogger (no reason to in San Diego) but everything I have used has worked fine and I am very happy with my GTO.