I had 2 monitors back around '85. Seemed like a good idea at the time, cool as heck and a complete waste of time: there was nothing I couldn't do as easily on one screen.
When I was on a project to sort out British Telecom's email network I had about 30 monitors stacked up in front of me, each one monitoring multiple post offices. It was amazing the speed at which the bars representing the mail queues could grow every time the mail backed up somewhere and began jamming the whole system
