Interesting! I usually have a stick of butter out in a butter dish on the counter until it's used up. It doesn't take too long for a stick to be gone - I doubt one has ever made it 48 hours.

What I can't stand is butter straight out of the fridge that you can't spread. I feel like my teeth are going through a lump of grease if I'm biting into a roll with a chunk of butter on it.

My butter hasn't ever tasted sour.