I used to work at FB and the huge, open offices were one of my least favourite parts about the job. I worked in the London office for a year and that was actually a little better because it's smaller and generally quieter there, but the three years that I did in the Menlo Park offices were not particularly fun for all the reasons described. It's very difficult to concentrate when there's constant background noise. Me…
There were definitely large benefits to the open floor plan back then since we were working on so many things and each person was wearing so many hats. It made staying in touch with people's progress really easy. We were also working 80-100 hours a week back then, so it was good to constantly stay in touch since there was so little structure and process back then.
I have mixed feelings about FB being held up as one of the models for open floor plans today though. While I think it was definitely useful at the time, I think the open floor plan has become less important as tools have gotten better. We didn't have tools like FB Groups, Phabricator, etc, so you had to be within earshot of your collaborators in order to make sure everyone was in sync.
My sweet spot would be team sized rooms if I was starting a company today. I used to be so jealous of teams that had to grab war rooms and ensconce themselves in there with a bunch of laptops and displays. Even though they were working super hard to meet deadlines, they looked happy as can be.