I don't think a blanket statement can be made about productivity and it's relationship to working from home. Some people have jobs that require collaborative thinking, teamwork, and relationship building - these people would benefit from being in the office of course, no arguments here. Organizations have invested untold millions in maximizing 'collisions' between staff to encourage this behaviour. However, there are also a great deal of people churning out repetitive, well defined administrative tasks - for these people, the interruptions of chit chat, long walks to the bathroom / shared kitchen, and other time wasters actually reduce productivity. To make these assertions, we need to look at specific jobs, environments, and even individuals to maximize our output.