Open floorplan works if the entire "open area" is engaged in a common goal. In that case, headphones can be more of a hindrance than a help.
However, in the case where the open floorplan is simply an office cost savings measure that puts mixed goals in a small collocated area, then yes, headphones..
I disagree with the common goal idea -- even if there is a common goal, there are often very different tasks. And there are still countless distractions from noise, etc...
The latter is so important, I'll risk a vapid comment just to second this. To echo the sentiment of a commenter below, you don't realize how miserable a mixed open office is until you are trying to do work with a standup happening 2 feet away from your head.
(Disclaimer; Microsoft employee without a personal office, quite jealous of those with.)
The place I'm at now is the only job I've had (or place I've contracted with, met with etc.,) that's gotten this right. The whole open floor plan thing, to work well, has to have a reasonably accessible way to escape it when necessary.
Open offices can only work, IMO, when there's a breakout room, or in general some sort of closed door room anyone can jump into and get things done or have a 4 person meeting. There's just no escaping the need to have privacy for the point of thinking, or even privacy for the point of talking. Maybe there's a perfect job in a perfect world where everything is open, but in my experience, there's a need to get away from the group once in a while, either alone or with a group.
Even that wouldn't work for me with open offices because I can't simply pick up my giant desktop and move in there to do work -- I'm completely stuck in the open office.
One conversation that I can't tune out, and I lose 20-60 minutes of work. I may not be cut out to work for other people, but it's intensely frustrating that by far my most productive hours every day are post gym/dinner between 10pm and 1am every night.
However, in the case where the open floorplan is simply an office cost savings measure that puts mixed goals in a small collocated area, then yes, headphones..