Seth Godin's latest post What happens when it's all on tape discusses how a person's behavior would be different if they were being video taped. Of course most people would act a bit differently.

The basis for this is the Heisenberg Uncertainty Principle. If you Google it you'll get a number of links. Most of which show the actual formula and get a bit technical. In laymans terms it means that "Any interaction between an observer and the observed changes both. The more an observer probes, the more difficult it is for him to obtain INFORMATION about the initial STATE of what he observers and the more are his observations contaminated by his own efforts"

All that physics in college is paying off!