The only major thing that went wrong was some electric component, which caused the car to break down. I'm not exactly sure what the component was, but it was something to do with the gearbox. It caused VW a lot of grief, as the dealer I got towed to, couldn't solve it themselves, and had to refer back to VW engineers in Germany. It was, they admitted, a very unusual fault.
It was fixed under warranty - a good job, because it involved taking out the whole of the dashboard to get to the component (not sure if they had to take the engine out). It meant they had the car for 2 weeks (I was given a hire car free to replace it). Contact via the dealer was reasonably good (although my hire car - a crappy Peugeot 207 - also broke down, and I ended up with a smaller engined, but far superior Renault Clio), and their general level of service was pretty good, as I have found to be the case with VW dealers I've come into contact with.
The only resultant problem from all this is the dash has developed a very annoying couple of rattles, which my local VW dealer are going to fix.
The speakers in the doors have not been fitted particularly well, and they vibrate on rough roads. Another thing the dealer is going to fix for me when it goes in.
I have the light coloured seats, which I love, but they are not child or water friendly. Water stains them quite badly, so I'm going to have to have a valet after I dropped some water on one seat. But they do look good in a black car.
I should point out that mine is a company car, so I only pay for the diesel, therefore I can't comment on cost of ownership, other than purchase price and fuel.
Options bought with the car:
* Cruise control.
* 17" alloys with 225 tyres (mine is the original GT, which only came with 16"s as standard).
* Centre front armrest (essential - comes with storage and a rear facing air vent and cup holders - worth the £100!). Very comfy.
* Highline trip computer (£40 well spent as well - gives you control over central locking and lighting, to name but a few).
* Extra tinted rear windows - subjective, but my Golf is black and it looks great. Also provides extra sun protection for my little boy in the back.
I've always wanted a Golf, and I've not been disappointed. First of all, here are my gripes and then good points:
* It's not that quiet on the road. A fair bit of road roar and engine noise penetrate the cabin. Annoying on a £20k car. I think it's down to thin insulation material. Not sure why this is. It's not too bad on motorways and doesn't spoil the car (i.e. it wouldn't stop me getting another). Could be better though (not as noisy as the new Civic, which was my other option).
* Engine is taxi-like when cold, but fine when warmed up.
* A few creaks and rattles (I've already mentioned this in the what went wrong section). Again, could be better for the cost.
* Ride - (not really a gripe) the GT TDi has sports suspension, so it's going to be a bit harsher than the regular Golfs. But it's not bad. It felt quite crashy when I first got it, but now the car is 17 months old, it's softened a bit and is fine. It's never going to match a BMW, but it corners exceedingly well (I have optional 17" alloys with 225 tyres, and they grip like glue in the dry).
* Speakers - the standard stereo (RCD-300) isn't bad, but the standard speakers aren't up to it, and can distort on particularly heavy bass. I wouldn't bother changing the head unit, but next time I'll get the speaker upgrade. Note: if you don't listen to loud or bassy tunes, then don't worry about it.
* No MP3 playback - as mine is an early 2006 model, the stereo didn't come with MP3 playback (annoying!) and no facility to plug in an MP3 player (you can get this on a Fiesta, why not on a Golf???!) but a £50 device from e-bay sorted this nicely, even though I had to fit it myself.
* Performance - very quick! 0-60 is 9 seconds, which isn't stunning by today's standards, but mid gear acceleration (where you need it!) is great. Overtaking can be done with ease and safety. It's excellent cross country, and I've easily kept up with an Elise on B-roads. Never maxed the speed, but it cruises easily in the 90-100 mph range (where legal!) and rarely embarrasses itself. It can often surprise other faster cars - even on the motorway :-) They don't like it when you go past and they see it's a diesel! The 170BHP version must be fantastic. Note: mine has the 140BHP, but rumour has it that VW are a bit conservative, and it's more like 150BHp. So 9 seconds may be conservative too, as it certainly feels quicker than that.
* Economy - when I first got the car, it was brand new, and so economy averaged about 42 mpg. Recently when I checked the overall average, I'm getting 47 mpg approx. Most journeys to work (18 miles mixed A road, B-road, hills, flat and traffic jams) gets me 50-52 mpg if I don't rag it too much (I don't hang about) and 43 mpg if I tear along. Not bad really!
* Comfort - the front sport seats are excellent. Supportive and grippy. Neither too firm or soft. Easy to get a good position, and I've never got out after a long journey feeling crappy. The Golf is surprisingly roomy. If I have my driver's seat set up for me (I'm a shade under 6'), I can easily sit behind myself without my knees rubbing up against the driver's seat.
Standard equipment is good. The self dimming mirror is handy, as are the auto sensing wipers (they occasionally get a bit confused, but far better than manual intermittent). It would have been nice to get stereo controls on the steering wheel as standard - like you do on many other cars of the same class. The option for this is a staggering £400!! The semi-automatic climate control is fine, and I don't miss the fully automatic version I had previously on my Passat.
Overall, I love the car, despite some of the faults. Dealers have been good, and as it's a popular car, there any many opinions and pieces of advice on t'internet. One useful website I found is http://uk-mkivs.net/ which has an excellent and helpful online community, with lots of advice and examples of how to mod/fix your MkIV or MKV Golf.