Mine takes forever to warm up as well and was thinking of replacing the thermostat, it does eventually reach 90 degrees but only when sat in heavy traffic. On the move it barely goes past 70 degrees which is too cool as far as I'm aware.
What i have learnt recently though is that the TDI engines do not actually warm up properly when sat idling for ages and need to be under load so it is best to drive them asap and even if the engine is still cold whilst sat in traffic it's best to put some electrical load onto it to help raise the temperature sooner.