On the other hand, I was wondering if any of you actually considers blown-out windows a mistake, in general, or what do you consider to be the "overexposure treshhold" for it.
Well, I tried to address this in my previous post. It depends on the look you're trying to create.
If you're trying to create a contrast range that's a "naturalistic" look (emulating what your eye sees), then it would usually look wrong to not see any detail out the window. The exception might be what David alluded to about distant windows (like at the end of a hallway), where it's reasonable that your eyes would be adjusted to the darker indoor light and not really see bright detail out a distant window.
If you're trying to create a contrast range that's more "photographic" (what film captures in real-life situations), then blowing out a window could look fairly normal, at least on a sunny day.
If you're trying to create a high-contrast look (like a skip-bleach negative), then you would expect the window detail to blow out.
I can't speak for others about an overexposure threshhold for detail outside windows, but generally for a "naturalistic" look you want the outdoors to go pretty hot but still hold some detail. The precise amount depends on the film stock/video camera you're using. On film you might find +3 stops or more looks fine, but on video you'll need to reduce that to +1.5 for a similar look (just as a comparison).
When shooting on location you'll often want to put ND on the windows to help get the indoor and outdoor exposures closer together. When shooting on a stage, you often want to put a lot of light on the backing or exterior view to make it look realistic and not "fake."
Perhaps David can tell us what he does on "Big Love." I haven't seen the show yet, but I assume there may be sets where you see the "studio" backyard out the window.
Like Michael Nash said, I also sometimes put Half Hampshire Frost on the windows to throw the view out of focus, which helps if you only have something fake-looking like a tree branch on a c-stand arm against a white background.
Thanks for clarifying that (no pun intended ). I looked up Half Hampshire Frost in the swatchbook and it's indeed slightly lighter, with more clear image showing through, than "Hampshire Frost."