Via Andrew Sullivan:
"Love should be treated like a business deal, but every business deal has its own terms and its own currency. And in love, the currency is virtue. You love people not for what you do for them or what they do for you. You love them for the values, the virtues, which they have achieved in their own character,” - Ayn Rand.
This is Rand the clueless dogmatist in pure form - that is to say, not 100% wrong but reality twisted until it's deeply and fundamentally wrong. Part of Rand's problem was that she didn't believe in instincts, and love is among the more fundamental human instincts. Certainly love has something in common with admiration - the actual name of the emotion she attempts to describe, but love is probably more likely to be the cause of admiration than the result.
The core problem, I think, is that love is fundamentally a matter of empathy, a human characteristic that Rand despised and plausibly lacked. The triggers for romantic love are doubtless complex, and include admiration, I suppose as well as lust, but I suspect that "virtue" is not exactly primary. I seem to recall a period in my life when I fell madly in love with any pretty girl who rested her head on my arm - of course not many did.
When one loves, I think, one identifies with the one loved, and sees common purpose with them. This is pretty useful, in the evolutionary sense, especially if you want to cooperate on some long term project, like raising a child.