Personally, to be honest, I use "dude" in my social life when I'm around friends. But I don't believe the word "dude" has any place in the professional business world, and thus you'll never see me using it in newsletters or articles, ever. Personal opinion.
However, I've seen more and more emails (and spam mails) reading something like this: "DUDE! You have to see this!"
When did all the marketers become surfer dudes? Just asking.