Interesting. I definitely do this with Coursera... but you haven't noticed any dramatic timing being thrown off?
Not really, in the sense that everything is half the time so the timing between things is still intact.
Are there some "dramatic sequences" in which I miss part of the intention of the directors/etc.? Yes, I'm sure there are. But for at least a large portion of the shows I watch, most of the important stuff is in the dialogue anyway.
Disclaimer: I'm probably a less visual person than most, which means I don't pay as much attention to the visual aesthetics of shows as others do. Also - some sequences even I don't watch at 2X, mostly action sequences and the like.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.