I've only had experience sharing a bed with girls my age. As a 6-7yr old, I used to share a twin bed with my friend. Tight squeeze, but on sleepover nights, we weren't exactly there to sleep anyway. And my friend was tiny.
I also shared a bed with a girl from my 4-H club. We were both staying in the spare bedroom at her Grandparents, the night before huge regional dairy show. I woke up when she turned over and accidently elbowed me in the face, but otherwise, I slept like a rock.
Though I usually sleep like a rock. As a kid, I'd be awake for hours on end at night, not anymore.
At my aunt's place, she didn't have a double bed for her spare bedroom, but she had a pair of matching twin beds. She put them side by side with no space in between, then puts the sheets over both beds. It's a double bed, but without the shaking. Though I stayed there with my Mom once, and she makes all sorts of random noises in her sleep. The train whistles that sounded like there was a track in the back yard didn't exactly help that night of sleep either...
I think it would be totally weird to not at least share a room with my husband (you know, that guy I don't know now, but might someday meet and marry...lol. My dating life sucks.). Though I can understand why couples would choose separate beds, especially if your partner kicks, tosses around, steals all the blankets, etc.