My breasts are two different sizes, but it isn't noticeable to the naked eye. I wear a size 36DD, but one of my breasts is slightly larger than that (and the other is slightly smaller). I settle for the in-between because the different really isn't big enough, like I said, to be viewed with the naked eye when I'm. . . naked. . . . it's something I notice when shopping for bras, when one breast fits perfectly in the cup and the other doesn't. I think all women have some variance/difference between them, though.
Otherwise, my body is pretty symmetrical. I have short arms for my body length, I think, just by an inch or two, but they're both that short.