Clay Johnson:

I’ve been using a second monitor for nearly ten years, thinking that vast amounts of space were key to productivity. The second monitor myth has been around for quite some time. Yet the only actual scientific study I could find linking multiple monitors to productivity was done in 2003 by a monitor manufacturer, a video card manufacturer, and the University of Utah. It’s actually kind of a marketing document, not a study. I’ve opted for one, large monitor. Two monitors just allows me to put distractions on one monitor, and actual work on another.

I found that to be true for me as well.