Some of you 170TDI owners may interested
I'm currently waiting for a new glow plug relay from Audi for my 2 week old A3. Interestingly it will be a different/modified version of the part from current which suggests a recognised weakness in the component - and hence an unspecified wait. The garage even had pictures printed off to show them how to identify the difference between old and new versions.
The symptoms are the glow plug relay staying on longer than expected given the temperature and then the yellow emission control system warning light (looks like a small engine) stays on. Luckily, hasn't stopped the car starting - yet.