On AA 1437 from LGA to MIA on Thursday July 22 we were stuck on the tarmac for over 3 hours. I actually nodded off and woke up a little while later thinking we were in the air, but we were still taxiing around. The captain announced that because of bad weather (thunderstorms) on route to Miami, his route had been changed by ATC and he no longer had enough fuel to go via the longer route, so needed to return to the gate to refuel, which took a while, then of course we had to wait for the fuel truck. After 3 hours it was announced that because it had been 3 hours, anyone who wanted to deplane could do so (we were parked at the gate at that point) but they would not be allowed to reboard. Needless to say, I was happy to eventually get to Miami (at 11:45 pm, originally scheduled 7:50 pm).