"Workers in open-plan offices get sick more often" - Only supported by one study done in Denmark. Not enough research.
"Open-plan offices are less productive" - Supported by a study which only identified some of the negative effects of a open-office plan (such as the effect of irrelevant speech). That study didn't attempt to measure the benefits of an open office, or attempt to exhaustively list all of the effects of an open office, so it doesn't speak to the overall effect on efficiency.
All the other claims were either focused on employee opinions or were about things other than an open office plan.
You can guess what my opinion here is. At my previous company, the floor plan had both offices and a wide open area, so we could choose where to sit. I picked the open area and loved it. Being able to eavesdrop on the status of other teams, or having really easy group communication (as easy as yelling across the room) was incredibly valuable. I think the open office is especially nice in our industry since we really tend to suffer from under-communication and a lack of cross-team networking.
Anyway some folks at our company chose small offices and I think they enjoyed it. The ideal floor plan would have a mix of both I think. But I don't think Facebook's new one-giant-open-area building is nearly as awful as people make it out to be.
My team was a cluster of 8 fixed desks in a giant sea of engineering, with people always walking through our area on their way somewhere else. The noise level was so high they installed custom white-noise generators that have an unnerving effect when you spend all day with them.
Contrasting this to another company where there were separate team rooms of 5-10 people for each group in the company and it was much more pleasant while still having a lot of the same benefits.