Both cases certainly happen here (Northeastern US). They're probably more common as an exclamation or a reaction to something in surprise ("Dude!" or "Dude!! Why did you do that?!"), rather than a casual, neutral question ("Are you going to the movie, dude?"). The last example would usually be between two men, but a girl could also say it to a guy. I haven't heard that example between two girls or in the case of a guy speaking to a girl--that would sound awkward.
Similarly, "guys" is used between men, women, and men and women indiscriminately. "Dude" isn't quite indiscriminate yet, but it probably will be some day.