I've actually done it. I enrolled in a charity run at SFG on the Great American Scream Machine. It was from 9:00AM - 7:00PM. We ended up riding it 114 times! They sealed off 1 car from each train for the people in the charity. We were allowed bathroom breaks and got free hotdogs and soda all day whenever we wanted!
If I were to do it again, I would proably do it on the Rockin' Roller Coaster at Disney's MGM Studios. Smooth ride, great music and AIR CONDITIONING!!!
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Beware of the Dragons! - Dueling Dragons
http://www.rollercoasterfreaks.com/