You are a great source of renewable energy, just as long as we can keep you eating protein and starches, maybe throw in some salt and salsa for taste. Now some clever folks at MIT think you can generate a lot of useful energy, not just use it for slamming your keyboard or pacing the floor of your cubicle.
In what the MIT brains dubbed "crowd farming," they've come up a concept to harness some of the energy generated by people in motion. Gives a new meaning to the phrase "under your own steam" perhaps. The concept relies on converting mechnical energy into electricity. Thousands of pedestrains pounding away on piezoelectric walkways is a huge step beyond the human-powered hand-crank radio.