I'm also one of those cases where *I* lost weight, but went up two cup sizes... A --> C in two months. One of the scariest things that's ever happened to me... but otherwise, I believe the tale is that the boobs are the last thing to gain weight, but they're the first to loose it
Skeeta: That ratio only works one size up or one size down. A 14B is more or less a 10C. However, an 8D and 12B are about the same as a 10C. You can compare next time you go to the shops - the cup size (as in depth and width and everything) is the same, but the band width is slighly different.
EDIT: I've seen 8 AA's in Sydney. Maybe even an 8A. But nothing bigger than that.