You are promoted to a new position which carries with it much more responsibility. How do you relate to co-workers who were your peers?

 If you were at the same level as they workwise and are now "boss" what should happen to that dynamic? Do you distance yourself somewhat? How do you discipline someone if/when necessary with whom you might have a close relationship? Do you lose friends and gain subordinates? Seems really hard to me. Any of you ever experience that?