I lived through Hurricane Ike and have several relatives who lived through Hurricane Katrina.
We went 14 days without electricity and I came really close to losing my mind. Two things I learned:
1. the worst part of not having electricity is not the lack of air condition (although that did very much suck). The worst part was the darkness at night. Basic tasks become impossible in the dark. Once the sun sets you go to sleep because there isn't much else to do. Flashlights are great until you forget where you put the flashlight and its pitch black. Cell phones are very useful for illumination until they lose their charge.
2. Ice is the most valuable commodity when you don't have electricity. Stores will eventually restock bottled water, canned food, ect... Ice was the one product that I saw people literally fighting over and huge pallets of it would disappear within minutes of being placed.
Another thing - if you are involved in a massive disruption you are pretty much on your own in that you cannot rely on police or ambulance to come to your aid - they are overwhelmed. One good aspect of the whole ordeal was that I met and *gasp* actually talked to many of my neighbors. It was interesting to see that human beings are actually quite good at banding together during times of extreme duress. Of course, once the power was restored we went back to our indifferent ways but at least I know my neighbors now!
Finally, contrary to popular belief, there was no mass hysteria, no large group of roving bandits breaking into stores or looting homes. I have a feeling that potential criminals knew they would have been shot on site because people were on edge. This is Texas after all.