The most productive period of my life was when I lived in our dorms at college. The dorms were arranged in suites of six small rooms, each of which was big enough to hold a bed, a desk across from the bed, and a nice big window at the far end. Each room was probably about the size of one of these little houses.
Outside was a common area where the six folks in the suite could gather, watch TV, hold parties, conduct mysterious pseudoscientific experiments, et cetera.
It was great. The secret is that when you wanted quiet, you got quiet. But then when you wanted to interact a bit, you opened the door. To interact a little more, wander up and down the hall. To interact even more, walk out the door into the common area. Then there were larger common areas in the lobby downstairs, the yard outside, the dining hall down the road...
I work in an open plan office now. My coworkers are great, but you can't have a phone conversation without being afraid that you're destroying the productivity of ten people, and it's getting increasingly difficult to focus. Which can make you really tired and lower your rate of doing work. There are times when I've had to start breaking out the headphones and the ambient music, which is a real sign of desperation.