I wouldn't worry about the regulator issue you can fix it yourself (
http://www.golfgtiforum.co.uk/index.php?topic=27944.0) or its only a few hundred quid from VW itself, and they might not break or have already been done anyway.
With my 1.8T I was primarily concerned with a) service history and regular oil changes as good oil preserves the turbo, and b) is it owned by a nob who has thrashed it.
After having owned one, if I was to buy another I would also check for...
1) Have the doors drooped, esp 3 doors.
2) How "crashy" is the suspension from worn bushes etc. (a bit pricey for a garage to fix).
3) My recaro's went a bit annoyingly creaky, so I would check for that.
Obviously theres all the normal car buying advice... Headgasket, oil burning, HPI, irregular tyre wear etc. etc. etc.