I would be careful. there is a fine line. long hair that is sort of side swept like "ryan sheckler" style is really hot. but long hair that is not layered and looks like a girl cut. i.e. flat across the bottom and straight is not attractive in my opinion. Also, most girls don't like pony tails.
Check out taylor kitsch. he is a good reference for hot long hair.
but as far as a reference for bad long hair, pretty much look up any screech metal band like slip know and you will see what I mean.
Right now I am letting my hair grow to my shoulder length. It currently is in the stupid stage. My ex-g/f (whom is very hot) told me it looks better on me than my old buzz cut hair due. But she also told me to keep it well kept, clean, etc,. I have also noticed I am getting a lot more attention from women than I used to. It all depends on how it looks on you. Go for it, experiment and see if there is a difference. Hope that helps