Oddly enough, I find that when I'm having a basic chat with someone, they always think I'm female. It isn't until I actually start talking about my interests or whatever that they think overwise. I think, maybe, it's the names I use on the video games I play(since my sister is generally the person who picks out my character names), but they almost always assume I'm female at first. Lol, then I get into a conversation about music, television, movies...and that's when I get A LOT of "Huh...wait...are you a guy or a girl? I thought you were a girl, but now I'm just confused."(especially when I start talking about Digimon or Ninja Turtles..)
It depends on where you go, in my opinion. I play a shockwave game called Inklink, and I get ASL'd there every 5 minutes(huge hookup place..but I just like the game), and unless you have a masculine name...you are automatically assumed to be female. In fact, I use a somewhat gender neutral name on there(in my opinion), and yet I'm constantly told to change my screen name, because it's not masculine enough. Which is unlike World of Warcraft, where I(and my sister) am automatically assumed to be male. In fact, even if I meet a girl on there myself, I honestly don't believe it till I see proof, haha.