GotchaThe trans in the WRX was originally purpose designed for a FWD 90hp car. It's been beefed up a bit through the years, but the main problem is that with AWD spinning the tires to waste extra stress on the driveline is less of an option. So instead the pressure finds the weakest point and breaks it. In the 5-speed, it's the teeth on the gears which shred and go boom.
Driven correctly, and in stock form, the trans is fine. However, if you are at stock levels and banging on the gears (not rev matching at all, or just dumping the clutch between gears regardless of engine rpm as compared to velocity and gear choice) it will break. There are people with +300awhp on the stock trans and no issues. There are people who break them stock. It's all about how you drive it.
I was very nice to mine, but on July 14th I was racing a friend and shifted into 2nd gear very aggressively - it went boom. Two weeks and $4600 later($3600 for parts, the rest for labor), I have a 6-speed from an STI in my car.