Not a lot! There is a gas leak in the air-conditioning system behind the dashboard, have been told it will cost $700 to fix as they would have to rip the entire dashboard out! I just get it re-gassed every 12 months as the leak is only slight.
The switch for the headlights fell off, but was easily fixed with a bit of glue.
The headlining caved in (a common Commodore fault) but again was replaced fairly cheaply.
The front doors (particularly the drivers side) move about slightly in their frames over rough roads or when hitting sudden bumps in the road causing them to squeak. A friend told me to moisten the door rubbers with vaseline (which at first I laughed at) and amazingly, it works. No more noises!
The engine idles fairly rough and sounds a bit asthmatic under load (with a bit of drive-line shudder) but these are typical attributes of any Commodore from the VN on wards.
Mechanically, the car hasn't missed a beat.
I am quite amazed at how reliable the car is, although it gets a service every 4-6 months without fail.
I fitted an aftermarket cruise control system which works a treat on long trips and helps keep my speed in check around the city.
I've also fitted a K&N air filter to give the car better breathing, and more performance! (Not that it needs it)
The interior is fine, if low quality. The instrument binnacale prevents air from the vents closest to the drivers side door, and from the centre, to blow freely onto the driver, which I see as a pretty bad design fault! (subsequently fixed with the VR)
The car can catch you off guard in the wet, due to the rear wheel drive/powerful engine combo. Have been caught out several times even when taking corners carefully in the rain.
Overall I am quite happy with the good 'ol Commodore. It's an excellent cruiser on long trips, has plenty of power to spare when you need it and feels like it will run well for many years to come!