I've recently had both of my bikes (non-Trek) serviced at Trek and they have been awesome. Very knowledgeable, pretty quick turnaround and called with any issues/updates.
One thing to note; you can't book in for a service, you turn up with your bike and leave it at the shop. From drop off to pick up I waited about 2 weeks.
After the service there was an issue with one of my bikes (torn lever hood) and Trek replaced it free of charge, and dropped my bike home when it was ready. Legends! Thanks Trek.