Buttermilk, buttermilk, how do I use thee?

During grocery shopping many sunny days ago, I came across a neat row of blue miniature milk cartons. Upon closer look (note: I don't usually wear glasses while grocery shopping), I realised that they were actually packets of buttermilk. I was like: "Ooh... so this is buttermilk, huh?" Without much thinking of how to use it, I just dumped it into our shopping cart. And now the forlorn little blue carton is sitting in my fridge waiting to be called upon for mission, but I still am clueless what I am to do with it. =s

What is buttermilk? According to The New Food Lovers' Companion : Buttermilk of times past was the liquid left after butter was churned. Today it is made commerically by adding special bacteria to nonfat or lowfat milk, giving it a slightly thickened texture and tangy (reads: sour) flavour.