Interestingly one of the pros often mentioned for open office space is that it enables collaboration, I've never seen that work out in practice very well, though. At least I'm much less prone to start a discussion with someone in an open office because it will disturb everyone else who are not interested in the topic. More often than not other people will hush you and so on.
So in the end an open office is detrimental to my health, happiness, productivity and (surprise) collaboration but hey I'm saving the company some thousand $$ each year, or am I?
I think many people experience that where I work. When I walk past someone in our open office they tend to look at monitor with work on it even if they were just looking at something else on another one.
Our management is the kind that could care less if we watched Youtube all day if we were keeping up performance, and I'm not even management (or close!) and yet people still feel a little bit of stress knowing someone is looking over their shoulder inadvertently.
That's your problem then! If people is judging you for going to the bathroom or browsing Hacker News instead of your results, then what the company/employees value is the problem.
People can browse internet at work, and if at the end of the year they are high performers I will give them an above average salary increase. If they are extra hours at the office, never look at Facebook but they don't perform well I will have a talk with them to see what's happening as that's not good.