Last weekend, I was at an event where coffee was served. After taking a sip, I reached for the salt shaker on the table on got the strangest looks ever, when I did one quick tap over my cup. That's when I remembered that it isn't common knowledge that salt blocks the bitter receptors on your tongue, masking any bitter flavour in your food. This is especially useful information for someone like me, who only really appreciates coffee for its caffeine content, and not so much it's trademark bitter flavour.
I also use this trick when eating grapefruit, which also has a bitterness. By shaking over a very thin layer of salt (as in, I could count the granules if need be) before I apply sugar, I can reduce the amount of sugar required by nearly two thirds.
And now you know.