I brought my 2008 TT Coupe into Canada in September 2010 with a little over a year of warranty left on it. I had lots of warranty work done on it before the four years were up. The local dealer had on-line access to all the service records done by the previous owner in Chicago, which was great because the warranty book had no stamps in it.
The owner had purchased Audi Care in the US, which was not honoured in Canada, but my dealer pointed out that Audi of America would honour it if I took it to a US dealer across the border, and it would be worth my time since it was a $1500 scheduled maintenance.
I had to get Audi of America to talk to the Service Manager in Bangor (who claimed that Audi Care could not be transferred to a new owner) and in the end, all went smoothly.