I've worked in offices with cubes, in co-working spaces, remotely (for a long time), and now in an open plan with around 200 people.. I have never been more productive than the time I worked remotely. The constant distractions in an open plan are bad enough with 200, I can't even imagine how it is with thousands.
I don't like people looking at my screens. I've never had a problem with the quality or quantity of my work, but as soon as someone see youtube open blasting out music. Hackernews, reddit, facebook all open, someone soon complains. That's just how I work.
I think of it like a sausage factory, the boss loves the product but doesn't want to know how it's made. Leave me to work in my own way.
I've never worked in an open floor plan with more that like 100 people. But I seem to recall only being bothered by people within a few cube sections from me in any direction. I would imagine that at some point the rest of the people in the "room" are far enough away that it doesn't really matter.
The collaboration that an open floor plan is supposed to promote has for me more or less translated to 'i can clearly see you so that is an open invitation to come interrupt you'. For me it's mostly that plus the constant movement in your peripheral vision nearby and far away that makes it bad.
