Computers are getting smaller and smaller and are using less and less power. It does make sense nowadays to look for ways to either decrease power consumption or look for alternative ways to produce power.
Back in 1996, Thad Starner from IBM wrote an interesting piece of article on Human-Powered wearable computing and explored quite a few ways how the human body could be used as a source of energy for computers.
We're not yet reaching 'Matrix' stage where humans WERE actually living batteries but one of the ideas which could be explored would be the use of keyboards as a convenient way of generating power to generate electricity.
The idea that I put forward is a keyboard with an integrated computer that is powered not only by keystrokes but also by mouse motion and light coming from the monitor screen. Back in 1996, a computer with a power consumption of 0.5w was feasible.
Current technology does allow such metrics to be reached while improving dramatically on general performance.