I’m a big fan of open plan offices, to the point that I have just asked for my cubicle walls (marking me out as a slightly more important person than the people around me, but providing no acoustic privacy, and reducing my natural light) to be removed.
I think the difference is that in my job, collaboration is important, and adds to everyone’s productivity. People learn and take in knowledge differently, but my experience is that if I spend an hour with someone explaining an issue to me, that time will be much more productive than if that person spent an hour composing a report, and I spent an hour reading it. Those interactions, writ small, are much more likely to happen if you can just wander over to someone’s desk and ask them a question.
Of course, you get the occasional annoying person who talks very loudly right next to you about the weekend, but if most people around you are polite and considerate (which happens surprisingly often in an office full of professionals who are treated like professionals) then it works very well.
The interesting thing about this for me, is that my reaction is similar to my reaction to the difficulty of making part-time work happen professionally. I believe that a significant part of my productivity depends on interactions with other people; if I’m not there half the time, then it’s very hard for those interactions to take place. For some jobs it works; many it doesn’t.