Sure, for some things. If you don't know your breast size you may inadvertently buy a 46 Double D bra when in fact you are a 36 C. Or vice versa, if you don't know your breast size, you may constantly be making self deprecating jokes about lugging around your huge gazoongas, but only have an A cup.
If you mean, does it matter in terms of desirability or attractiveness to the opposite sex the answer is somewhat complex, and more of a: sort of. For the most part guys are more interested in the perk, firmness, and overall shape of the breast. How do these breasts look in a shirt, in a bathing suit, in my bed, etc? They care about shape and handle.
This is not the same as sheer mass. It's not like your breasts are cold cuts and the best pound for pound deal always wins. Most guys would rather have ¼ lb of thinly sliced prosciutto then 2 lbs of bologna. So in this regard size doesn't matter: it's the quality of the cut.
But, in respect to body ratio, yes breasts matter for many folks. Some guys like thin women with dancer-small boobs. Some guys drool over tiny bodies and huge boobs. Some guys like large women with large boobs. Some (I must believe) like large women with relatively small boobage.
I will end by saying guys of a certain age, usually under 18 and those who are still only getting their perception of what is hot by watching 80's comedies think huge boobs are synonymous with great. But as men mature, their interests and attractions spread out and diversify. Rest assured guys and gals of Guyspeak County, there is a titty for every man out there.
Now, doesn't that make you feel all warm inside?
It certainly does!
Having hated my boobs since I got them, it's nice to hear someone, who is not a friend or relative say this.
I love my boobs!
I'm a large woman but I'm only in a B cup... I should really be in a D to look normal. It makes me look all disproportioned. It's a hard life I live :(
Amit is right, bigger is not always better. I had the unfortunate problem of maturing very quickly during my early teenage years, and though my girls are HUGE, they do not look all that great (because guess what, stretch marks are not just for moms, and the heavier they are, the more gravity takes a toll, no matter what your age). It sucks because I always feel like I'm disappointing the man in my life - he sees what he assumes are amazing boobs underneath my shirt and can't wait to see them unveiled, and then.... fail. So if you've got smaller breasts, please don't complain. You could have ended up like this instead. I am more comfortable with myself now, but it's still crappy. :/
Good posture helps. Seriously. Like a cup size and a half of visual difference.
I'm perfectly happy with my bra size. Although my ex had the nerve say that he wished they were bigger.
My saying is if a guy is really unhappy about how you look... and it's somewhere like that, I kick them to the curb. I don't need that crap on something that is considered as-is in this way. I keep in good shape, good character and if someone is that focused on your looks that much... fine, don't need them either because 20 years from now (or sooner!) looks won't matter as much as a sense of humor, character and how he cares. If he fails on those completely, I don't really care much for him. If, apparently my small breasts were a total deal-breaker, I would find that depressing and he'd be out, no if and's or buts.
I have little ones, like I have a 26 band size technically, so not much volume, but I'm in good shape and fully prescribe to the there's a set for everyone. I'm just peeved a bit that I cannot find nice things to wear... but that's a different discussion. :)
Kudos to the funny guy!