Tweet Privacy Groups

It would be really nice to have privacy groups on twitter. For example, I have followers that I am friends with in real life and follows which I've never met. It would be awesome if I could select that a specific tweet is only public to my real life friends group. (Ex: "Anyone want to go out for dinner tonight?" is something I might want my 20 real life friends to see but not the followers I don't know.) Simply create a group and add some followers to it. Tweets would send out public by default, or give you the option to select a specific group.