Placebo buttons are buttons that actually do nothing except give the user an illusion of control.
The advent of computer-controlled traffic signals make the walk buttons at pedestrian crossings on heavily trafficked streets obsolete. By the late 1980s, most (but not all) walk buttons in New York City have been deactivated yet people push them anyhow, either in ignorance, out of habit, or in the off chance the buttons did work.
Many large office buildings also have dummy thermostats to give office workers the illusion of control. Some even go as far as installing white-noise generators to mimic the hum of fans after the HVAC system is shut off.
The same goes for the close button in elevators. Most elevators built or installed since the early 1990s don't have close buttons that work, unless you have a fireman's key. People do push them anyhow, because the fact that the door eventually closes reinforces their belief that the button works.
As for people who press P-T-W buttons consistently, I like to equate the number of times a person presses a P-T-W button is directly proportionate to their impatience and therefore their unintelligence. No way does pressing it more than once help. I see youngsters yelling at the street light: Come onnn! Reflection on video gaming?
However, downtown most of the lights are constantly in "walk mode" (including the wonderful "Denver shuffle" - http://www.urbandictionary.com/define.php?term=denver%20shuffle ), so in this part of town there are no buttons to push.
Some of the newest traffic signals around town in fact have an audible indicator (a sort of "thunk" sound) and a red light that comes on in the middle of the walk button when it's been activated, so if you're approaching an intersection to cross, you don't have to wonder or go pressing the button 15 times just in case.