I would like to point out that donor milk is often hard to come by. I've used it before, when I couldn't pump enough for my DD. My friend offered, but still, she was nursing HER baby as well and could only provide me with ~4 oz a day. To buy it, it costs about $4 an OUNCE. Not saying it's not an option, but it's not as simple as "oh, of course I'd use donor milk"! There's websites like milkshare that help connect people for that sort of thing, but the women asking way outnumber the women donating. So unless you have like 6 friends who happen to be nursing at the same time and all willing to donate a little milk on top of nursing their own little ones...hate to say it, but you're using formula.