My MK7 GTD has just ticked over 20,000 miles and I still have 4mm left all round on the Bridgestone Potenza S001's it came form the factory with. To be honest, the Bridgestone's have always been crap for grip and tramping but wanted to get some use out of them before swapping.
Even thought they are not down to the legal limit, they are slipping more than they used to (if that's even possible), so I think a change of tyre is on in the new year. My shortlist so far are the Continental Sport contact 5's or the GoodYear Eagle F1 asymmetrical, but whilst I don't mind sacrificing some mileage for a better gripping tyre, (say around 15k miles), the stories I'm reading of tyres shot in 7-8k miles is a bit shocking !