I would ask my students, "Do you think we (Americans) are dirty?" And I would get a mixed result of "yes" and "no". Then I would explain why we don't, and that we actually do take them off later in our separate rooms. I made it a point to say that while I am in Korea I practice taking off my shoes at my house and when I visit other people in Korea.
All of this prompted me to put up a poll on my site. However, I can't really say where my respondents come from.
For those 4% who don't wear shoes, well I just hope you have some tough soles.
*You can check out this poll and past ones at the bottom of my blog.*