Jason absolutely nailed it. The reason why you can't get work done is simple: there are way too many interruptions in the office. Meetings (the worst interruption of all), email, IM, people walking into you area to ask a question (do you have a second?), phone and so on.
After I watched this video I did a mental exercise and I came to the conclusion that none of my output in the last 6 months occurred while I was in the office. It either happened before I went to the office, after I came home or on the weekends. My time at the office is busy but not productive. I need some quiet, uninterrupted time that I cannot get when I am at the place I am supposed to "work".
It's about time we reward productivity and output rather than busy work and face time. Assign tasks, give people freedom and make them accountable for delivering.
If you have an office job I am sure you will relate.