In general they are very helpful but I wouldn't leave one of my bikes with them again.
I paid for the highest level service (~£850 inc. New breaks) for my trail bike, the frame was damaged during the service and they didn't bother to tell me about it.
They used what looks to be flathead scewdriver to open my headset, so that area of the frame is surrounded in chips now.
I wouldnt recommend trek for anything that requires your bike be left unattended. They have lost my trust for 1. Damaging my frame 2. Not owning up to it.