I actually paid the single supplement once - this on the Holiday cruise when I took my mother-in-law along with us. In that case, I stayed alone in an outside standard cabin while my wife, her mom, and our son stayed in the Cat. 12 suite. Before the cheap comments cascade.....it was my mother-in-law's first cruise and she was 78 years old at the time. There was no way I was going to leave her alone in a cabin, and there was also no way I was not going to let her have the best accomodations. She is a wonderful human being and I am not just saying that!
Anyway, I liked having a regular cabin to myself. But I doubt I'll pay that premium again.