I'm in an open floor plan space with about one hundred desks in it and it's never particularly distracting to me. I barely ever even have to use headphones to concentrate. People simply don't have loud distracting conversations. It'd be different if I were mixed in with salespeople having phone conversations from their desks all day every day, but we're all engineers. I appreciate being able to easily ask my coworkers a question as it occurs to me immediately.
OK, fair point. I did once get rearranged into an open plan office where all the teams were intermixed for I-still-don't-know-what reason. Half the staff was sales, and yeah, it was impossible to concentrate. Fortunately, we had a liberal work from home policy, so I had a means of escape when I had a deadline approaching. But I still only lasted for a few months after that.
Just to reiterate, I don't think the open plan office was really the fundamental problem. It was the attempt to mix oil and water.
