Of course, this only worked because the work I was doing during those times also required very little coordination and communication with other people. I'm introverted enough that if I have my own space but need to get out of it to talk to someone, I'll find myself procrastinating doing that.
Having a shared open plan office makes it harder for me to focus, but easier for me to interact with people. I'm not sure if that's a net win for my productivity or not.
The best people on a project should be on the least important parts. The second best people lead the important projects, and thus grow to the best. In the mean time the best people are on something that isn't that important anyway, so if someone has a question there is no reason not to interrupt them and ask. This also leaves your best people free for when marketing has another "great idea" so they can ask before promising the impossible (and in some cases they can get something now instead of waiting for the entire project cycle)