When it's cold I wear socks in the house. My husband wears slippers. In the summer, I go barefoot as often as possible, and my husband switches out his slippers for flip flops.
At other people's houses I generally follow their lead. For most of my friends/family, no one wears shoes in the house. Shoes go in the breezeway and we all wear our socks inside. In the summer, when it's not slushy/muddy, I'm usually wearing sandals and I think I can go either way -- taking them off and going barefoot in someone else's place, or leaving them on. Just depends on whose house it is.