fklwmn: It's mostly worrying about interrupting them in the living room, since that's where they stay most of the time. My other roommate wasn't home for quite a while, so they were not disturbing her out in the living room. I do usually knock - not loudly if it's very late because I worry I'll wake them, and then I'll open the door very slowly so, if they didn't hear my knock, they'll probably see or hear the door opening and I won't get the bird's eye view of whatever they were doing. Thanks for the input about the scarf or what-not over the doorknob - if this gets to be a huge problem, I'll ask them about it.
rdge: My schedule and Allison's schedule (in terms of classes) are sort of similar, so we're home pretty much at the same time. They save their playtime for late at night, which I had the displeasure of waking up to before they moved themselves out in the living room

. I know there's rare times when I'm not home, like when I go and hang out with my friend, go to school for reasons other than class, or elsewhere. I guess I feel weird asking her about any sort of schedule because I think their chances to do anything romantic are scant due to everyone being home, as well as roommates' friends coming over.
stanthedevil: Allison's BF living with us is not a problem financially. We live in school-sponsored apartments and we do not pay rent in the 'normal' fashion. Her BF lives in the same building as us, so he doesn't need to be signed in or anything, and his staying with us, as far as I know, does not impact the cost of utilities. As far as the situation I had been discussing, though, I think they chose early morning hours for themselves because they figure no one is going to be awake at that hour...or if they are awake, will not have a reason to use anything outside the bedroom. It's kind of hard to avoid them because the bathroom is right next to where they have their sleeping area set up, and to get to the kitchen I need to pretty much step over them.
Thank you all for your advice in the matter. I'm thinking I may just have to allow them to get embarrassed when I'm having a bathroom emergency.