i'm of the opinion that if the girl really wants them and it makes her happy then by all means she should do it. we have come a long way with plastic surgery and it can be very very nice looking.
Personally, I don't have a preference one way or another. I've been attracted to women who are A cups and women who are D cups, size isn't a major factor for me at all. What really matters to me is that a woman is comfortable with her own body, so if that means breast augmentation then by all means, she should do what she wants.