I agree with valleyquiltermo who said that it is rude to take someone's time without asking. I've had drop-ins who stayed way too long and ruined my plans for the whole day. And perhaps it is a flaw in my personality, but I feel very uncomfortable when folks drip in and my house is not clean and neat. I realize that THEY don't care, but "I" do....and I can't relax and enjoy their company. THEY don't care if their house is presentable....so they don't think others should care either. It all comes down to, "Different strikes for different folks!"
I've also been visiting a friend and someone else dropped in and took over the conversation.....and there I sat. Not much fun!