I've been an avid gamer for over a decade, mostly playing the Battlefield franchise of shooters. When I worked as a programmer, there were a bunch of us that would end each day with a couple of intense matches.
When Battlefield 3 was released last year, the only computer I owned that could run the game was my work iMac. So I installed Windows 7 on a Bootcamp partition, and spent many evenings gleefully sniping pilots out of planes as they tried to take off. Yes, I'm that guy, sorry.
But a funny thing happened as time went on. It became easier and easier to stop working, and start playing. Having the game so readily available made it really difficult to focus on any task I didn't enjoy. I found myself "needing a break" more frequently.
Recently I upgraded my work iMac, and took the Battlefield equipped computer home to be our primary family computer. A funny thing happened. It became extremely easy to focus on work at the office.
I believe that mental associations are a powerful element of productivity. If you begin to associate your working space with things other than work, it affects your view of work itself. When I come into my office now, it's for work and my mind accepts that because it has no choice :-)