I try to follow whatever protocol I can spot. If people clearly take their shoes off before entering their house, I'll do the same when I visit. If they walk around inside in their outside shoes, I keep them on. Personally, I slip into "house shoes/slippers" as soon as I enter my own house. The bottoms of my shoes that have been all over the MBTA do NOT need to be all over my clean rugs! We do have two dogs, though, and I simply have to turn a blind eye to whatever germs they're carrying around.

In therapy... I'm guilty of that dreadful socks and Birkenstocks look in autumn. And by dreadful, I mean wonderful. Socks will slip out of Birkenstocks quite easily. :-)