"Breasts are usually asymmetrical, meaning that one woman's breast may be a different size or shape than her other breast. Interestingly, a woman's left breast is usually a little larger then her right breast, though this is only a generalization. (It is also quite common for men to have one testicle that is a different size or shape than the other)"

From: http://www.afraidtoask.com/breast/breastsize.html

I've never even looked to see if mine are different sizes. Thanks for the interesting post, Angel!