When the girl is wearing the the correct size, D or DD cup breasts are not as large as many people think. The models on something like bravissimo.com are all at least that size, but they don't look out of proportion to me. Apparently there is a tendency for larger-breasted women to wear a band size that's too big for them with a cup size that's too small. So they might think they are a 38D when they're actually a 34F or something like that.
Having said that, I love the look of a larger chest, especially when dressed well and carried with pride! The number of times I see women with a lovely curvy figure wearing not only the wrong size bra (creating the four-breast effect of flesh spilling out of the cups, eek!) but unflattering clothes, it makes me sad. I think there are many ways of dressing big boobs to look elegant - it doesn't have to be glamorous or corsetted, although that can be nice too!
Obviously, this is just a preference. I don't recommend partner selection based on breast size alone, but to each his/her own!