I assume these are only at teaching hospitals, but please correct me if I’m mistaken. But even at teaching hospitals, how common are those observation galleries that they’re always sitting in, looking down at the surgeries from on shows like Grey’s Anatomy? Surely there isn’t one in every OR?
They’re definitely not universal. I’ve been in OR’s that didn’t have them.
I’ve been in a few ORs and I’ve never seen one. My husband performs surgery almost every day he works and they don’t have them at either of the hospitals he works at, either. But I don’t think those are teaching hospitals, either.
I was born in a teaching hospital, but have never been in one of their ORs. And it’s 2,600 miles away so I’m not going to pop in and check 
This is just my opinion . . .
My impression is that observation galleries are a thing of the past. They were very common, almost ubiquitous, in all the hospitals I trained in. That being said, I can’t recall seeing one in any modern hospital (at least that I’ve visited or had surgery in!)
Privacy concerns and modern information systems (i.e. web cameras etc.) have probably made them obsolete.
According to my wife, both Brigham & Womens and Mass General in Boston have multiple ORs with galleries. She believes most of the big hospitals in Boston do as well. She also said that residents don’t discuss their sex lives while observing surgery, so GA got that wrong.
We don’t have observation rooms/galleries at our joint. I think this is something you’d see only at a small minority of older (mostly teaching) hospitals.
Not to mention medicolegal concerns.
I’ve seen old paintings (photos?) of surgeries in which the surgical area was basically a stage surrounded by stands in which the audience would sit. I’ve wondered if they had vendors selling snacks and if the surgery went poorly, whether there was booing and people throwing things.
For example, Thomas Eakins’ painting The Gross Clinic shows such an open theater. But that was in 1875. For contrast, see his 1889 painting The Agnew Clinic.
But where will Junior Mints fall from?
These types of observation rooms are much less common. At major teaching hospitals, procedures can be recorded (with consent of course) and then are available online or rebroadcast in a classroom. Some procedures are broadcast live. For example, here you too can view surgeries just like a med student!