[tobiasu]

I think that's a bit low. According to WA 100kcal are ~120 watt hours. The real problem is of course that us programmers hang around in chairs all day and probably need about 75kcal. Slow walking may increase that by (generous) 50kcal, of which say 75% are lost via body heat etc.

So http://www.wolframalpha.com/input/?i=50+kcal%2Fhour+to+watt+... gives us 15 watt hours. Subtract mechanical losses etc. and we may get 8-12 watts without breaking a sweat. Enough to power an ARM board or similar, but not the display.