Both front electric windows stopped working, a common fault with cheap plastic clips breaking. VW will repair free of charge on cars up to 7 years old (not officially). Or D.I.Y., buy new clips and regulator for £40 each side; the new replacement clips are all metal and so will not fail.
The clutch started sticking, resulting in a clutch master and slave cylinder and clutch replacement. This is another pretty common fault on MK4's. This was a more expensive fix.
The brake pedal switch failed (an £11 part, the replacement part has improvements) which gives 'Check Engine' message on MFD, which first time round is concerning, but a very cheap fix if it goes wrong. This is another common fault.
The engine coolant temperature sensor stopped working, causing the gauge on the dash to start moving up and down all the time. It is also detrimental to mpg, which dropped by up to 10mpg. The replacement is £70 fitted at the dealer and is an improved part.
An excellent car as a compromise, this car is pretty rapid and offers excellent fuel economy (47-52 mpg with Shell V Power Diesel, slightly less on others). The Shell V Power is recommended if you like the car to be virtually smoke free even under hard acceleration, and gives better combustion efficiency and continuous engine cleaning (so say Shell, but after £500 worth of the stuff used I would agree), which is good for the PD injectors, which run very high pressure.
The handling is another compromise; the car is very good on the motorway and dual carriageways, but can feel very soft and reliant on ASR when pressing on down B roads. So if you only drive down B roads and want one, then get a quote for Eibach/KW or other high quality German suspension for more sport orientated driving.
The paintwork and interior are both in excellent condition for a 6 year old car, and will probably continue to be for a long time. The seats are very good if you compare to a Focus or Astra of a similar age and mileage. Especially if you value being ache free after any journey (I am 6ft7", so very accommodating).
This is overall a very high quality car, with some very minor faults, and is very cheap to run considering depreciation, as the car holds its value better than any of its competitors. I expect it to run to a fairly high mileage, as I have a long daily commute.
The dealer I use has been excellent, and I guess some negative reviews may have been due to a poor dealer experience (another VW main dealer I used locally was 1/10).
When buying a used one, make sure it has full VW service history and you should have a good problem free car. It also makes the dealer more willing to help you out if anything does go wrong.