I come from the southern US and we use buttermilk in all kinds of things. It's a staple of southern food. I could never drink buttermilk straight from the jug; but I knew plenty of people who did.
We use buttermilk in cornbread, biscuits (in the US it's more like a savory scone served for breakfast), pancakes, breads, and cakes.
It's also used to make certain kinds of creamy salad dressings (like Ranch or Bleu Cheese dressings).
And I can't forget one of my favourite desserts:
Buttermilk Pie! Mmmmm! It's great served warm with a little whipped cream or ice cream.