If you've got a long, thin face with masculine features or are the artistic type, long hair would work for you. Most guys can't pull off long hair because they look like underpaid I.T. workers or basement dwellers. I keep mine short because I can use my hair to frame my face and give it a bit of extra angular definition.
My brother's a music student at uni and has grown his hair out. He's got a long, thin face and has curly hair, which makes his face appear a bit wider. He's had lots of girlfriends despite his average facial features because of his devil-may-care personality, artistic aspirations and long, wild hair. By contrast, my cousin has long hair and it doesn't suit him at all. He's got a round, pudgy face, has average looks and wears glasses.