One of the things I found the most appealing about cold fusion, way back when the feasibility was still up in the air, was the possibility of many decentralized power sources in place of a few massive power plants.

While some people have designed "neighborhood" nuclear power plants, I still feel a lot more comfortable with nuclear plants in a few isolated and guarded facilities rather than scattered everywhere, regardless of the safety issues.

If fuel cell technology improves, easy decentralization may still be possible. I could see homes getting electricity from their own natural gas lines (already in place). Some cells already "burn" natural gas (I still am not sure exactly what happens to all the carbon.) Most modern large power plants also burn natural gas. What's the difference in efficiency between cracking natural gas in a home fuel cell, or burning it in a central power plant using conventional means and piping the power over wires? I have no idea, but I would really like to know.

And of course, there could be solar cell breakthroughs that make them cheap enough to put on every roof. They're slowly getting there. No carbon problem there, although some environmentalists get the willies thinking about the chemicals and processes required to manufacture solar cells.

Like cell phones, or for that matter hybrid cars, I think there will come a point when the technology and costs turn a corner, and suddenly everyone will have it.