Private offices or open-plan: which makes employees most productive?

I know Joel Spolsky has been very vocal about private offices being best for engineers. But do you think being a private office might feel lonely after a while?

Which plan has the perfect balance of being able to focus and at the same time, being the most productive? Private offices for each employee or have an open plan and noise cancellation headphones? :)

"It depends" on what you mean by productive.

If you mean the ability to crank out hundreds of lines (of code, copy writing, whatever) then solitude will help most people.

If you mean the ability to get work done, but understand that having other people around can be a positive stimulus, then open plan will help most people.

The right answer, is of course somewhere between the two - aka *both*.

A year ago I opened a small coworking space. Coworking in the true sense - not a hangout, but a group of different people, from different companies, sharing space, but getting on with their work, most of the time. We have open space, and some side rooms, they get used as people feel necessary.