Auto-tune works wonders with the human voice. You don't have to sing on key, in fact, you don't have to sing at all - just speak your lyrics like Mister Rogers.
It's no wonder there are so many contemporary musicians who sound good in the studio, but can't carry a tune in a bucket when you see them live. With the magic of technology, all you need is decent biceps and a pretty face, and you can be a pop sensation too.
Having said all that...when used for good and not evil, like in the Mister Rogers song below, auto-tune is really cool.