I posted a link to Live Journal article by a guy who is as strict (probably stricter) as I am about removing shoes at the door. He intends in the future to adopt the Japanese practice of having separate slippers to wear in the bathroom. This idea does make a lot of sense. The bathroom is probably one of the least hygienic rooms in the house. Keeping the two floor spaces separate would be a good idea.
Hence, I remove my slippers when I go in the bathroom. Of course, this strategy might fall down in the summer when I do not wear slippers. If I had my own house or apartment, then I might get separate bathroom slippers or flip flops, but not now. With my father being Obsessive-Compulsive about tidiness, I doubt he would like my leaving extra pairs of slippers around the house.