If anyone watched the show Jericho, they did something that I liked better than what some other movies/TV shows have done; after the nuclear blast, which fried unshielded electronics like computers, modern cars, power plants etc, they still were able to get older cars w/o electronic control systems up and running. I think they even eventually were able to get some local power back for things.
We live in a modern society with a lot of tech, but we also have a lot of knowledge. If something happened and the main power grid failed, you can't tell me that there wouldn't be engineers hooking up small wind, water or sun powered houses and buildings. Even steam powered. I can't picture a modern society not coming together and rebuilding. Unless something really catastrophic happened.
I guess I'll have to see how they write this new show, Revolution, to see if I buy into it or not.