I'll try to help since my Jetta is basically a Golf with a trunk.
Things to look for:
Power window problems (if equipped, since it's a GL, most likely not). They like to cause headaches.
Sunroof (if equipped). They like to leak and jam up.
Make sure the central locking works and alarm arms/disarms.
The rear defroster doesn't have a timer so be sure to turn it off manually.
Even though the fuel door looks like it has a remote release, it doesn't. Just push on the fuel door at the point nearest the rear passenger door and it'll flip open. Sneaky.
The 2.0 is a good motor, although a bit slow, especially with automatic. No real issues with the transmission.
The A3's are blessed with a nice climate control system (IMHO far superior to the one in my old Contour) but it does have it faults, for example the AC condensation drains on A3's love to plug up. The drain flap is accesible through the firewall, albiet not "easily" accesible in a TDI due to the turbo.
Be careful when changing a front turn signal bulb, the housings are plastic and the mounts can break rather easily.
Timing belt. Like the TDI engine, the timing belt in the 2.0 needs to be replaced at regular intervals. 60,000 miles (or 96,000 km) is the interval in the TDI and I assume the 2.0, not sure. A broken timing belt in either engine can lead to nasty results so make sure you replace it on time. Be SURE to replace the tensioner too, not just the belt.
VW waterpumps are one of the weaker points. Give it a once-over when you replace the timing belt, since you're going to be down there anyways.
Not sure when VW switched but the more recent A3's and the current A4's use a special coolant mixture that while it looks like red Dexcool, it isn't dexcool and is only sold through VW dealers. DON'T mix it with Dexcool unless in an emergency.
Be sure to get a Bentley repair manual. I have one and it's bar none the best for VW's!
