The limited screen real estate made it really easy to stay focused on my work and not get distracted by HN and Reddit. :)
Personally I find great to have a full screen editor/ide without floating file list and symbols one one monitor and documentation/shell on the second. When you look at one you are not interested in the other so I would not call it multitasking but easier process switching.
People who keep the mail client open should try notifications: events versus polling is much more efficient for low clock human beings.