How often do you drop in on your married friends a week, especially unannounced?

I often wonder how guarded people are about their privacy. How often do married couples get together with other married couples? Are such get-togethers informal or always prearranged? I see people being friendly at work but they do not seem to socialize outside of work. I have neighbors, but we never invite each other into our houses. My wife and I do not have friends outside our immediate family. I think we are strange, but perhaps not. We are both foreign-born and do not share religious affiliations with most people around us. Is this a factor for our seclusion? Do Americans feel ill at ease around people with foreign accents? I am confused.