Actually, I realized some time ago that I like men with long hair because I’m attracted to men with some feminine characteristics. Likewise, I like women with short hair because I’m attracted to women with some masculine characteristics. I sometimes think my long (mid-back length) hair makes me look more feminine and traditional than I actually am, but it looks much better on me than short hair does, and it saves a lot of time and money on haircuts. And I think my lip piercing negates any “traditional” effect. 
My understanding is that it has to do with sexual selection.
Like antlers on a buck deer, or gorgeous plumage on a peacock, well-maintained long hair imposes a survival cost (see the link above) on its owner while also demonstrating health in a clearly visible way. Sure, it’s not a very high survival cost to have long hair, but it’s there.
As the link says in more detail, there is some tension between sexual selection making an animal more distinct from the other gender (dimorphism) and more noticeable (survival cost) versus natural selection pressuring an animal to blend in with others of its kind and not to be noticed by predators…although it should be undertsood that said tension can be over-emphasized.
Sailboat
Forgive me for stating it this way; But I’ve always felt that hair length can be a key to a woman’s “consistency” (for lack of a better word). Flaky woman will always have short hair (“Oooh, I want it short today… Oooh I want it long today”) Since it takes a considerable time to grow really long hair, it’s evidence that she can make up her mind and stick to it. If she can’t make up her mind, then her hair will always be short.
Parsing carefully… please note I did not say all short haired women are flakes. I just think all flaky gals will have short hair.
Wow, you never met a flaky long hair girl? I love long hair but I just cannot accept this statement. I believe you either have a small sampling or you are projecting or something. There is even a commonly recurring character in fiction of the crazy or eccentric older woman with long grey hair.
I guess I don’t try to read too much about another person by the length of their hair. I just know long hair attracts my eye much more than short hair.
Jim
You need to get out more. My ex-wife has long, gorgeous hair. She’s a dear, sweet woman, but she’s an utter flake. Flaky enough to make Tony the Tiger weep with envy.
I like having long hair b/c it gives my boyfriend something to pull during, umm, our “recreational activities”. He likes me having long hair b/c it gives him something to pull during those times. I can’t speak for anyone else, so YMMV.
It’s fun, though. Good times. I think well-kept, short hair looks really good on women, but I’m learning over time that a lot of things that I (and other women) think are necessary to be attractive are things that men don’t give a damn about. Again, in my experience.
I’ll put in another male vote for short hair over long. Long hair can definitely look great too, but a cute woman with a very short haircut will grab my attention right away.
As to why that is, I can only come up with one reason beyond simple aesthetic preference: A woman’s neck is a very sexy part of the body for me, and long hair tends to cover it up.
I think it’s this more than anything. There’s more involved than just the woman looking younger; it makes the man in her life feel younger also, or older if she perms it up or bobs it.
I’m attracted to women who are highly intelligent. When I see a woman with short hair, I feel sure that the odds increase that she’s a smartie. Now, I’m not saying that all women with short hair are intelligent, or that all women with long hair are dumb. I’m saying that women with short hair tend to be more intelligent than average.
Ditto for women who wear little or no makeup.
Oh, and eyebrows. To me, nothing says “help me figure out how to spell my own name” than overplucked eyebrows.
It comes in handy for draggin’ her back to your cave.
I think women can look good with either, but a full head of really nice hair cascading down can simply be very pretty. Toss it over just right, and it goes from pretty to way sexy. It’s also very nice to touch if it’s soft. I really don’t care if it’s traditional or not, beautiful hair is beautiful, and if there’s lots of it, lots more beauty. Sorry, hope this isn’t offending anybody! Is it wrong to like something that’s really quite lovely in a wonderfully feminine sort of way? Again, I could give a crap about traditional gender roles if they’re absurd, but I like what I like.
I’ve been thinking about this some more, and I think there’s more to it than simple looks.
Women can wear their hair longer to disguise or camouflage parts of their face and neck that they think are suboptimal, so some women look better with longer hair because of what you’re not seeing.
Some women look better with short hair because they’ve got good features for it.
Some women would look better with longer hair, but wear it short anyway; and vice-versa.
Therefore, the examples of long haired vs. short-haired celebrities may be flawed due to self-selection. Maybe the question is better answered by imagining short or long hair on a woman who, in other respects, you do not otherwise consider attractive.