This is an interesting topic! For me personally, the only time I would ever do that is when I'm at my parents' house. We're very close and they don't care if when I'm over there that I grab a pop from their fridge or go on their computer or watch their tv.. and same goes for me. When they come over, the first thing my dad does is turn on the hockey game lol. But I also am not married and I live with my sister and we are a very close family.. I call my mom at least once or twice a day. That's just how we are. I have a key to their house and they have a key to mine, but we only use it in case of emergencies, although I know for a fact it would not bother them one bit if I stopped by while I was in the area while they weren't home (say for example to use their washroom or grab something that I left there). When they come over to my house, they know that they don't have to knock, they can just come on in. I would never do this sort of stuff with my friends' or other family members (such as aunts, uncles, cousins). I have one really close friend though who is over at my house a lot and she knows she can grab anything from my fridge while she's here. She rarely does, but it wouldn't bother me at all if she did because we're such good friends and I want her to feel at home while she's here. My other friends though that I'm not as close to, I guess it would feel a bit weird. As for walking in without knocking, it's never a problem here because the city I live in is very high in crime and no one ever leaves their door unlocked.. even during the day! So my friends/family (with the exception of my parents) would have no choice but to knock.. otherwise they wouldn't get in (unless I accidently left my keys in the door... which I am notorious for doing!)