I've been thinking about buttermilk for a few days now and came to a realization after a quick consultation of wikipedia. What is buttermilk (the cultured variety, anyway)? Basically, it's milk that has been treated and thickened with bacteria that create lactic acid. It's thick and sour. Then it came to me, that's pretty much what yogurt is, isn't it? So really, cultured buttermilk is really just milk that's half on its way to becoming yogurt!
I've actually taken to using it like I would yogurt in a variety of ways. Take a glass of buttermilk, sweeten it a bit I like to sure stevia extract) and add some vanilla extract, for example. You have yourself a vanilla yoghurt smoothie-drink-type-thing.
May use a whist to add in some jelly, or maybe sweeten and add cocoa powder for a chocolate yogurt/buttermilk drink. They may sound weird, but they're quite good!