I think I'm seeing lots of misconceptions about boho and also about volume here. To me, boho has more to do with materiality, texture, pattern, and design than with silhouette. There are a lot of voluminous boho designs, but they are not the same thing. Angie gave a good summary above and notice the word "volume" didn't come up in the description. Peasant blouses are usually a looser cut, but they are still not a uniform style. Even though they lack structure, they are still tailored...which brings me to the next point...
I suspect that a lot of people who say they can't wear volume (which again, I emphasize is not necessarily boho) probably can, but either haven't tried it it at all, haven't tried the right garments, or just haven't gotten used to it. Volume is wonderful. As long as it's tailored at the shoulders, it's a great comfortable and forgiving option. I am not thin or straight and I wear volume well. It makes my chest look smaller and completely hides my midsection. It does hide the waist, which in my case isn't a bad thing, but I think it looks great even on the queen of tiny waists (Tanya) and also on Angie. Emphasizing the waist is a flop proof, timeless, flattering option, but it is NOT the only option. It just takes some adjustment, much like faded jeans. I don't think the look is for everyone and if you're dead set against it, then by all means, embrace with your waist-flattering garments. But don't knock it until you have tried it and given it a fair chance! Also, not all volume is created equally. It does require some experimenting and if you're really not into it, then it probably isn't worth the hassle.
Anyone from the ye olde days remember this top? This was my first experiment with volume and I loved it (still do):
http://img.photobucket.com/alb.....G_0948.jpg
That's pretty extreme. But something like this is still loose without being as dramatic:
http://www.target.com/gp/detai.....M=Clothing||B001OCILLI&CPNG=women&ref=tgt_adv_XSC10001
Angie, please feel free to correct me if I'm wrong about anything here. I just feel like everyone is getting volume and boho confused, and misunderstanding volume in general.