Well, I don't think discussing the meaning of beauty is useless even if you agree you can never quite get at it because a better-informed opinion about something is always, you know, better... There certainly is a lot of writings in the subject of beauty and/or art, and this is actually my main reason for studying philosophy.
Anyway, there's a case to be made that beauty (more specifically, an "aesthetic experience) occurs at least in part at a lower level than something so highly structured than the ego, so it isn't necessarily subjective.
And even if it's completely subjective or if the "hardware information" can be overridden by society there's still some gain in talking about/studying it. I mean, if you didn't you wouldn't even arrive at the conclusion that beauty is subjective.
In some cultures, women are partially crippled by having to wear high heels for extended lengths of time. This makes them desireable.
In other cultures, women smear chemicals all over their faces, to change their complexion, or put unnatural colors around their eyes. This makes them desireable.
Another culture has their women get their asses surgically altered, to meet an accepted standard of beauty.
It's a good thing we're not a primitive society like the Mursi or anything.
This is why I don't really ever bother with trying to define some kind of objective or specific definition of "beauty". It varies too much over time and cultures. It's like trying to define "art"; largely useless, and inevitably devolves into wankery that derails the conversation.
Nail on head. Beauty is a reaction you have to something that happens. Art is a reaction you have to something that's made. Both subjective, regardless of how popular the opinion.