Now granted that I am a 1975 baby...
I have had long hair since around age 10. It got to a point that it was just wrong to have short hair and I made it known I wanted long hair... It took a while but I don't think my hair has been cut since I was erm, 15? Somewhere around there, as a result my hair is basically the length to reach the small of my back... Personally, I'm going for a bout knee length
The only downside is my hair is both thin and light... can we say medusa?
*giggle*Needless to say I'm very much a fan of long hair, on girls and guys both.
But in addition to what Dennis mentioned about guys with long hair is, at least in my experience, is that there is a stigma attached, or at least that is what I have found.