1. Rattling interior bits and trim
2. Alarm gets wet and needs replacing because it doesn't beep
3. Gets hot spots on rotors from moderate braking ($496 replacements under warranty)
4. Differential pinion gear shimmed incorrectly. ($1641 for entire differential assembly covered under warranty)
5. Seats feel like trampolines
6. "Alcantara" on door panel fading and showing signs of wear
7. CD player likes to skip first few seconds of every first song when changing from 1 CD to the next, not to mention it still "jumps" or "skips" from time to time, even on flat pavement. It's very sensitive to any little flaw on a CD.
8. Brake dust is attrocious.
9. Stock wheels already have little rust dots and starting to pit from brake dust.
10. Harsh ride
11. Widespread problems with struts rattling around on 2005 models (never had this problem)
12. 2006s break motor mounts because they were liquid-filled to reduce vibration.
13. Not cheap to tune
14. Not easy at all to work on
15. On the expensive side to modify
16. HORRIBLE paint
Regardless of the intricacies, I love my STi and don't plan on ridding of it anytime soon.