Have had the 66TDI in the household since new back in 2011. It has done over 105,000 kms with more issues than you'd hope of a 'German' car (let's just blame the South African build). Initial impressions are positive, as the car looks properly screwed together, the interior is very premium, and the drive train is very refined and generally quiet.
Unfortunately, in typical VW fashion, it all went downhill from there.
At around 30,000 kms, the brakes started shuddering, to the point where the steering wheel would shake violently during hard braking. VW refused a warranty claim for this, so new front rotors and pads were fitted at our cost (although, not at the VW dealer).
The original fitment tyres (Continental PremiumContact 2) wore very quickly and needed to be replaced before the 40,000 km mark.
Numerous issues with the diesel particulate filter (DPF) and numerous check engine lights, as well as frequent stalling in neutral (sitting at traffic lights, rolling up to an intersection etc.) and the smell of burning oil entering the cabin via the A/C eventually led to VW replacing all four injectors under warranty at around 70,000 kms.
The front shock absorbers were replaced about 5,000 kms ago, as they were both leaking and the car crashed over bumps. This was done out of warranty at our expense.
Can't wait for the next service, as the timing belt needs replacing. That's another $1000+ into the VW money pit that was, on paper, an affordable, economical, comfortable car.
There are some positives though, believe it or not. When it's working (not very often) it is extremely economical (averages under 4.0L/100km on the freeway), drives nicely, has stacks of torque (230Nm), the gearbox is solid and nice to use, and the car is very comfortable. In fact we've done a trip from Melbourne to Sydney with three people on board, plus luggage, not only in comfort, but all on one 45 litre tank of fuel. Not bad.
Would I recommend a diesel Polo of this vintage? No, absolutely not. Would I buy the recently-updated Polo in 81TSI manual guise? I probably would, although there are still some better options out there which may be a bit more solid on the engineering front. Grab a Mazda 2 or Renault Clio.