Life-stage of occupants: The only time I got a bit finicky when people left their shoes on at my home was when I had an infant at the crawling stage. I couldn't help but think that my kid would soon be rolling in, playing on - or, even worse, chewing - whatever the soles of our visitors' shoes were tainted with. With this still vivid in my memory, I always remove my shoes when visiting households with babies or toddlers.
Owner's request: It goes without saying that if the host or homeowner asks you to remove your shoes it's polite to comply without a murmur. Only advanced age, holey socks, serious foot problems or other health issues can be used as a compelling reason for retaining the footwear.
Purpose of visit: If a guest arrives for a social visit then leaving their shoes on is fine at my place. On the other hand if someone is touring a house (as I have done on dozens of occasions in the course of my work as a writer for interiors and lifestyle magazines) then shoes should be off since they'll venturing into private areas of the home. Similarly if someone comes to your house in their capacity as housekeeper, cleaner or nanny then I'd expect that these people would remove their shoes. Again, they'll be constantly on the move and likely to be trekking into many zones of the house. Those who regularly work in domestic settings will often swap their street shoes for soft-soled slippers upon arrival at the residence.
Setting: At a farm house or other rural property it's second nature for everyone to ditch their outside shoes at the door probably because the chances of unmentionables being present on the soles are high. Similarly, in the mountains or other snowy places most of us are inclined to leave our heavy boots on the porch.
Type of footwear: Work boots, gumboots and riding boots must always be left outside the door. No one wants mud or horse manure tracked through their house. For similar reasons, footwear used for gardening and outdoor sports should always be removed, too. And unless the floor is already battered beyond belief, stilettos should never be worn on a wooden floor for fear of denting it.
What are your thoughts on shoe removal? Are you a "shoes off" or "shoes on" type of person? What do you expect from visitors to your home? And how do you behave when visiting other people's houses?