I live in an apartment (by myself) and have all my stuff in the living room, so of course it's not completely quiet 24/7. For starters, I do the bulk of my critical cd listening and dvd viewing to the hours of 12am-4am. All my neighbors are nice and quiet by then, but of course my daily schedule gets a little messed up <sweats>. I like listening in the dark anyways; no brain cells wasted on visual perception! Next biggest annoyance as you mentioned is heating/air, I generally turn it off during critical listening peridos. My apartment is really well insulated in the side of a hill, so no problems there. Next is the damn refrigerator that goes on and off, I'll turn that down to the lowest settings (1 out of 10 coldness) if I have to, though I don't bother for dvds. Finally, we have my computer that sits next to my headphone rig, but I built it myself with quiet parts and it hasn't annoyed me enough to shut it off yet. Plus I need it for dvds since it acts as an external video processor.
When I take the above measures, I'm pretty satisfied with my listening environment. And of course for casual listening I don't bother.