When I went into the Army I was amazed at how the black guys called each other ******.
When I was teaching in the inner-city, my kids used that word all the time-and I cringed every time they did. Finally I told them that to me, that was the worst, nastiest racial epithet that could be thrown around, and I'd appreciate it if they didn't use it. It led to a discussion about why it's okay for black kids to use it but not white kids, and how they would jokingly call me 'my n*gga' because they liked me but I would have never, ever used that term to describe one of them no matter how much I loved them (which I did.) It was a very interesting and eye-opening experience for all of us.
That being said...I have never, ever heard a white person address anyone with that word. I don't know any white person who would use that word.