In open offices, I just used to put head phones on, listen to non-vocal music and be super focused for many hours.Being visible from behind puts stress on you. You may not be aware of it, but it will catch up with you before you're 35. Headphones don't help for that. It's not just the noise that makes open-plan offices so terrible. Booth-style open-plan offices would be a step up, but nearly as expensive as private offices and since this open-plan thing is really about cheapness (and back-door age discrimination, in some cases) that does not sell it.
Teams in open office often go to lunch together, have more personal exchanges and have far more socialization
This has more to do with the people than the office layout. There are open-plan offices with eat-at-desk culture and there are private-office layouts where people eat lunch together and play board games after work. Private offices don't mean that there aren't open spaces when people want them.
In private offices, I often see people catching up on news websites and FB and in fact I even knew a guy who freely admitted that he spent entire days on YouTube.
I spend more time goofing off in open-plan offices, because I have to hide the goofing off. Here's how it works for me. I have a certain amount of goofing off that I need to do per day, just because I'm a curious person (it's not actual "goofing off", it's just not immediately work-related). In a private-office layout, it might be 10 minutes every 2 hours spent checking the news, on HN or Reddit, reading a poetry book on the internets, whatever. In an open-plan layout, it takes 20 minutes to get that 10 minutes of goofing off in, because even though I don't actually need to hide it (I'm senior enough that I could pull the "so fucking what" card, and no one cares anyway because everyone goofs off a little bit) I still feel that social pressure.