I'm pretty flat - 34A and perfectly fine with it, though blouses tend to fit funny because they're always too big in the chest (and fortunately, I rarely need to wear them, so I'm not forever getting clothes tailored).

I've never been so thankful to be small chested as when my shoulder was broken and I could barely put a bra on, or when my back was stitched up and I couldn't wear anything tight over the incision.

And let me tell you, I definitely miss Patagonia's Barely A/B bra.