From The Economist online:
PLACEBOS are everywhere. Drugs firms sell red pills because customers are convinced that they are stronger than white ones. Pressing the button at some pedestrian crossings makes no difference to when the green man appears, but makes us feel proactive. And the “doors close” request in a lift serves no purpose other than to soothe the frustration of impatient riders.
Add another placebo to the list: thermostat controls in hotel rooms. An investigation by the Wall Street Journal has confirmed what many of us already knew deep down: “It’s not your imaginations. Hotel thermostats often aren’t under your control.”
In other words, fiddling with the buttons will make no difference to the temperature—although, given how effective placebos are, some people will feel a phantom cooling or warming in the room.