Is it really that weird? I say it to pretty much all my girl friends, and most of them don't even bat an eye, but there are some that I know that think it's weird and are all like "I'm not a guy. Why are you calling me dude?"
I always use it to mean "person," but maybe I've just been hanging out with a bunch of weirdos all my life and the vast majority of women are uncomfortable with it. Tell me what's up, guys and gals.