I have a couple of non-active friends. Strike that, they're non-athletic, which is something quite different. We're friends because we share other traits and likes, but also because we both are passionate about something. It doesn't have to be the same thing, but we understand having an overwhelming interest in something.

This sort of links to the Facebook discussion, of friends who "like" activities they don't understand. I tend to get passionate about a lot of things I do, and I like it when others are like that, even if I don't understand their things.