I've once inappropriately seasoned my coffee with a whole teaspoon of salt, which I happen store in an unlabeled Tupperware container next to my granulated sugar. A mouthful of salty coffee was not a pleasant start to my morning.

In small amounts, it can do wonders if you're not big on the taste of bitterness in your coffee. I first heard about the idea from one of my favorite chefs, Alton Brown. He has written a bit about it in his blog.