Once upon a time I was night owl. Okay, not really, but I used to stay up past 10pm on weeknights. I've been more of a morning person than a night owl for as long as I can remember--you try working in bakery in high school and see what that does to your sleep schedule--but I would still stay awake for prime time television.
Now? I might as well be called grandpa with the hours I keep. My usual bedtime is now closer to 8pm no matter what time I'm getting up (4:45 for a medium long run, 5:45 for a shorter run). Having a weeknight get-together at 8:30? Don't expect me to show up. Dinner at 7:30? Can we move it forward at least a half hour?
The thing is, I don't mind my old man bedtime. I seriously value my sleep and consider it an essential part of training, but I'm sure most non-runners (and probably plenty of after-work runners) thing I'm a few cards short of a full deck.
I'd like to say that once marathon training is over my sleep schedule will return to something that let's me watch 30 Rock when it's actually on TV, but summer's coming up: if you want to beat the heat, you have to run before the sun comes up!