That must have been pretty scary for everyone. I was once in a supermarket when all the lights failed. Fortunately they got a backup system going very quickly which at least allowed shoppers to leave safely, after paying for their goods, of course. Me - I just dumped my basket and headed straight for the exit!
I had the same thing last year. Thought it was quite exciting personally. Bit of a pain for those currently on the checkouts though I imagine - they were still rebooting the tills when I went to pay about five minutes later.
In 2003 we had a massive power outage which affected the Northeast and Mid West. Over 55 milllion people were affected. We had no power for 2 days, but what was really scary was finding out our cell-phones wouldn't work, you had to have a land-line. Also, it originated in New York so initially there were rumours abound that it may be a terrorist attack (post 9/11 just 2 years earlier) but you couldn't find out anything because no phone/computer/tv. It was just like you see in the movies. You don't realise how much you rely on electricity until you don't have it.