Something's happened this decade, slipped by mostly unnoticed, a small cultural thing, a permutation in the ever-twisting word-mash of slang.
"Dude" became gender-neutral.
"Dude" is following the path of "guy", or to be more accurate, "guys". Whereas "guys" has long been used to address mixed groups, as in "You guys want to go out for a beer?", it never really was gender-neutral in the singular. Not too many people would address a female friend with, "Hey, guy, what's up?" But "dude" seems to be taking that place of sexless singularity. I read it and hear it addressed to females all the time, often by other females themselves, usually in that inflected, faux-surferspeak - "Dude, what were you thinking?"
I don't know what it means, if anything, but it's an interesting little twist, nonetheless. Hey, Dude, wanna go bowling?
I'm the Dude. So that's what you call me. You know, that or, uh, His Dudeness, or uh, Duder, or El Duderino if you're not into the whole brevity thing.
- Jeffrey Lebowski