It's rather odd, but though I would never drop in on someone without calling, I don't mind at all when someone pops in on me. I love to have company,and my philosdophy is that if I can live in my mess 365 days a year, you can stand it for a few hours.
Actually maybe that is because my house is rarely very messy. A little cluttered with raising 3 grandkids, but never dirty. I love people, and would hate to miss seeing an old friend or family member, just because they weren't able to give me any advance notice. The only time it has ever been a problem is when they arrive, just as I'm headed out the door for something I can't get out of. I guess, "to each his own", but I'd sure hate to miss out on seeing someone for the last time, just because they felt they couldn't drop in because they hadn't called first.