The first time we were singing "How Great is Our God" with mics, electric guitars, and Easy Worship projecting the words. When the power went out we just kept singing. It was one of those aha! moments when you realize that you don't need all of the "extras" to glorify your Maker.
The power cycled back on at the end of the song, so we went with it. As I hit the last chord on the electric guitar the power went away again, and cycled back on again. My pedal reset to the 1 setting which is a crunchy loud distorted sound. I kind of let it ring out and then just smiled and everyone laughed. (We usually don't have much "crunch" in our service)
The power cycled back off and on again while we had our soldier who was back home from Iraq presenting his slides. He tried to show his pictures, but the power cycled off and on again about 3 times. I felt bad for this, but he kept going the whole time and he did a great job expressing his burden for kids in Iraq. In spite of the distractions, we had a wonderful service.
One thing I did notice - he was using a laptop to review the pictures as he was telling his story, and since the laptop was running on battery he could keep going even when everyone else was in the dark. :)
How would your service be different if you didn't have any power?