i bfed all of mine, still am ds3, they were all soley bfed till 9months and i never gave any extra vitamins, breast milk is designed for babies, why would nature leave out something that the baby needs?
also tho there is not as much iron in bmilk, the iron that is in it is much easier for the baby to digest and absorb, unlike in vitamin drops etc, which are likely to cause constipation.
i think the la leche league site has some good info regarding this