Just getting in on this discussion-
I'm 5'1", about 114 lbs, but short-waisted and curvy (34D). Currently, I can wear size small shorts in several brands (Giordana, PI, Performance), but jerseys sizing seems to be much less consistent.

As it happens, the Performance bike shop had a huge clearance sale, so I tried on a pile of jerseys this morning. I tried on 2 Pearl Izumi jerseys: One was way too large and one was way too tight esp. across the bust. Louis Garneau, too tight. Sugoi, med fit was ok (I just didn't like the design). World Jerseys, fit just right. I have 2 Terry and 1 Twin Six and 2 PI medium jerseys that are about right, but 2 other PI jerseys that are a different cut, and a bit snug across the bust. And the free kit (Hincapie) we got last fall from our training El Tour de Tucson? I needed a size small jersey in that one.