The GMR was a instant favorite of DF and I, until we looked at all the hidden fees that go along with having a reception, as well as the logistics. You cannot start your reception until 2 hours after MGM park is closed, so you're looking at serving your guests dinner at 9:30 or 10:00 p.m. There is an $8,000 mandatory entertainment fee, a $3000-$5000 venue rental fee (can't remember but it's somewhere in that range) and if you want to have a DJ set up in the ride, that is a $7,000 fee. This of course is all before food, beverage, ceremony etc. We decided that the cost would far outweigh the benefit and we couldn't feel good about spending that type of money even though we and our families could afford it. That's just a lot of money to be at a location as well as the time our guests would have to wait to eat. I wish it were different, we were really hoping to use it.
We have instead booked our reception at China Pavilion at Epcot. I think it will still be a very unique experience for our guests and that's what our goal was.
Good luck in whatever it is you decide. Those figures I gave you are accurate and from my Disney Coordinator. They are 2008 prices. I can pretty much garruntee that the prices have all increased for next season. Good luck and let us know how you make out.