This topic may have been addressed, but I don't see it off hand. Will Tesla service centers offer free charging for model S owners? If so, would this be on a drop in basis or would a reservation be needed. Where are the hours of operation for these sites be posted?
I've always been able to charge my Roadster at various Tesla locations. I usually call ahead to make sure they have a bay available inside and/or nothing blocking an outdoor HPC. Tesla has always been extremely accommodating.
My thinking is that chargers at the service centers should be very accessible and 24/7. In addition to the HPCs they should ultimately have a supercharger station or two on site. That being said, they may not want visitors at their service center after hours.