At IT Partners we are very keen on the subject of productivity. Some changes we have implemented because we have felt intuitively that they aid productivity, such as dual screens. We found it very hard to find any research supporting this until recently. The New York Times recently ran this article which discusses research by the University of Utah.
The research makes a big point about the actual display configuration and user setup, which is why in our office we use the Ergotron Monitor Stands. Everyone in our office has a laptop, and one of the great features of the HP Elitebooks (models with the P designation and dedicated graphics) is their support of dual monitors with a docking bay.
Once you get used to two monitors, you start to think of the times when it would be handy to have three – not possible… until now with the HP USB Graphics adapter.