I'm a guy with short, brown hair. I usually spike it all up. I've gone through loads of hair styles over the years. It used to be down to my shoulders, then I had a real emo sweep. After that I got a mohawk (about 4 inches high). Then I settled on having it short and use wax to spike it up. When it gets a bit longer it starts looking more like JD from Scrubs. Then, when it's too long to use wax, I get it cut. I'm always tempted to grow it again but always end up bailing.
I have it short and spiky, and used to have a mohawk, because I'm a huge fan of punk rock. I wear skinny jeans, band t-shirts, have lots of tattoos etc, so it just goes with my... image (I hate that word).