I plan to breastfeed (crossing my fingers I will be able to) for several reasons... Not the least of them being that I hear it's better for the baby and I don't see the point in buying formula when I can supply my own stuff! Lol.
That said, I know there are several reasons beyond mommy's control that can sometimes prevent breastfeeding. One mom on the pregnancy forum had to stop because of her little girl's jaundice.
Personally, I think every mom should at least give it a shot. Sometimes it works, sometimes it doesn't, but your baby can be very healthy either way.