I guess 'long' for me is one you get to or past elbow length, even? Mainly because that seems to be more rare in terms of how long girls grow their hair out -- longer than that is nice, however once the hair just starts to get to that curve of the lower back, then it's definitively 'long' in my book.

What I find so sexy about it (among other things) is, like JJ perfectly stated, the movement. Swinging, shimmering, shaking about as a woman moves: that's just so incredibly alluring.

For me, 'long enough' is just somewhere around the butt: either just a bit above or a bit below.

And as others have said: you really do need to make a movie about it if you do anything substantial -- I have no doubt it'd be your best selling movie to date.

That being said, I wouldn't go any higher than just about your butt, of course, you'll still be gorgeous either way.