Yesterday, I posted that on Sunday night, I tried to stream an episode of 24 in prime time, got a blurry stream, stopped and restarted the stream, and then got HD.
Last night (Monday), I did the same thing: Started an episode of Orange Is the New Black around 8:30pm, got a blurry stream, stopped and restarted the stream, and again it worked -- I got HD on the second try.
A) This is a good thing.
B) Based on other things I've read here, it does make me wonder if the problem is indeed related to the initial steram quality negotiation that the Netflix app on the Apple TV performs with the Netflix server. It's possible that sometimes, when Netflix is under load, that negotiation logic doesn't work (or maybe Netflix doesn't respond in time), but trying a second time, or third time, etc., eventually results in a successful stream.
I don't have the answer, just sharing another data point.