I have very narrow shoulders and a small bust. I have children's shirts that are too large in the shoulders. A shirt I bought from the little boys' department, which fits me well in the shoulders, is one size bigger than the shirts my ten year old brother wears.
This has its advantages, as I can (or at least can try to) shop in both the kids' and grownups' departments.
However, it also has its disadvantages. Because my arms are so long compared to my shoulder width, I generally have to choose between proper shoulder/bust size and proper sleeve length. That boys' shirt I mentioned, for example, doesn't even begin to cover my wrists. I wear the sleeves pushed up as half-sleeves. Another disadvantage is that I can't express any dissatisfaction with my body without someone shrieking that I'm so tiny and I should shut up.
I have heard over and over that people want to look like me. I don't understand it, really. I think that being my size actually makes buying clothing harder, not easier, than if you're more normally sized. For all the yelping about teeny models, there aren't any clothes out there to fit skinny people. Or if there are, I haven't found them. And if your clothes don't fit, it's very hard to look nice. Hence why I sew.