It's awesome to work in an open plan with other people who are working on THE SAME THING you are working on, and it absolutely sucks to be surrounded by people who are working on completely different things.

Also bad: not being able to find a place to work together on something with other people.

And the worst: not being able to find a quiet place to concentrate, when you need to.

I think the answer is a combination of quiet offices with very many small conference rooms that can be claimed for projects... and a large, anything-goes space (like a cafeteria) for when you don't mind complete chaos.