Most of what I write is done in first person. Since I'm not a man, my first person is definitely written as a woman.
Like Heather wrote earlier in the week, I may not be the most girly of all women, but I am a girl. Of course, unlike Heather, though, I do own skirts and dresses. But I also own combat books. (Hey, this brand of boots is very comfortable!)
When I really need to write from a male perspective — usually because a male character is speaking to my protagonist — I ask my husband how he would say... whatever.
It works for me. At least, I hope so!