Out of interest the same thing happened to us at the 12.01 am Screening of Revenge of the Sith at the Garden City Cinema in Perth Western Australia.
During one of the scenes, the film melted in front of our eyes. Everyone got upset and eventually someone from the cinema came and told us the same thing had happened in one of the other cinemas. He also recommended a toilet break whilst they tried and fixed the film.
It took them about 15 minutes. There was quite a bit of commotion and angst. When he told us it would not be long, again, there was lots of chanting, countdowns, clapping of hands (cricket style) etc until it finally did come back on.
The projectionist had to adjust the frame's as we had two halves of the movie on the screen for awhile. This took him around 30 seconds.
The official explanation was that due to a electrical thunderstorm outside there was a power spike that damaged the projectors and thus the film.
Anyway our first viewing of the Revenge of the Sith will be very memorable!