Although I have known for quite some time now that raw milk was vastly superior to its commercial cousin, I recently learned something new: raw milk does not go bad! It will sour (or "clabber" which I've read about it historical cooking books and never knew what it was), but it does not go rancid like pasteurized, homogenized hormone laden grocery store milk. After it clabbers, it can be kept up to six months and subbed into any recipe in place of buttermilk, yogurt or kefir. How awesome is that?
If it's at all possible for you to get your hands on raw milk, please do!
(Many thanks to Sarah, The Healthy Home Economist for sharing her wisdom!)