I work in an open office, and everyone wears headphones for hours when they need to concentrate.
The thing is, these people are doing irreversible damage to their hearing. Listening to headphones at a volume that will drown out conversation is not a good thing.
Furthermore, I've never experienced as many migraines as I have before switching to an open office. I have to keep pills at my desk. Never had to do that before.
Utterly impossible to concentrate on things w/out headphones.