I was there today for a charge, since there wasn't enough charge to get me home comfortably (arrived with 18 miles left). Anyway, I took the last available stall, and next to me on both sides were customer cars that were in for service - they had service number tags hanging on their rear view mirrors. I thought that this was rather bold of the service department, as I expect that they have charging stations in non-public areas. Anyway, after a while, two cars showed and had to wait, so I walked over to the first car in line and told the driver, "The car to the left of mine is there from the service department and has been there for longer than me, and I only have 10 minutes left." He got out of his car and walked into the SC, and a few moments later a service tech came running to pull the customer car out of the stall.
Seems to me that if the service department is going to use customer charging stalls, then they better have a better handle on managing them (ie: make sure that no customer is waiting for a stall, remove the car in a timely manner - not all cars need a FULL charge!).