My first reaction to this story was, well, if you suck energy out of people's movements, the people themselves will just need more energy, in the form of food, which is energy-intensive to make, so you're really not getting any net gain. Conservation of energy and all that.

But then I remembered that Americans are, ahem, fat. That is to say, they consume way more embedded energy than they can use, and it ends up as cellulite. This is, in part, because we don't get any exercise.

So, say you made floors flexible, and the weight of human foot traffic drove generators. Those floors would be incrementally more difficult to walk on, providing just a touch more exercise, and creating just a touch of energy. The cumulative energy gained, and fat lost, could be substantial.

To salvage a larger point out of this rambling: we have no shortage of energy. The sun casts more energy onto the planet than we could ever use. The trick is learning to tap into the energy flows around us in a way that's smarter and less destructive.