I've suspected it for years, but now there is proof. Breast Feeding does not make your baby smarter. Intelligence comes more from the environment you are raised in than from nutrients in breast-milk. Some babies may be more genetically predisposed to be smart, but that is also not from the breastmilk. Breastmilk will not change what is in the DNA.
I hope you take the time to read the article for additional benefits that breastfeeding does have for both the mom and the baby. And if you are feeding your baby formula, don't worry. Make a stimulating learning environment for your baby and he will be smart.