Long hair on some guys looks good especially if it's well kept. If it's not kept well then you can look....well....like Ted Kazinsky(sp) who is commonly known as the unabomber. What a fool that guy is. I mean he's got a full head of hair and look what he did with it!!
(No I don't think the unabomber is funny so don't post my quote back asking that).
If I had a full head of hair ala Teddy bear Kazinsky I'd consider growing it out long if I could pull off that look. Ask an independant opinion if you think you've got it. If not then cut it short like the rest of us and be happy you don't have to deal with curling irons, color treatments, and hair sprays.