Having spent some time in recording studios, I was aware that automatic pitch-correction software exists and is used by nearly every singer to smooth out the occasional off note. (Neko Case claims she doesn't use it, but she's the rare exception.) But I don't sing, so haven't spent a lot of time with it myself.
So I was fascinated to hear New Yorker music editor Sasha Frere-Jones, who wrote about pitch-correction this week, give an audio demonstration of Antares' AutoTune software in the magazine's Out Loud podcast. He sings a version of Kelly Clarkson's inescapable "Since You've Been Gone," sounding a bit like Lou Reed until he gets to the chorus, which he actually comes close to hitting. (Try it. It's hard.) He and the audio engineer pitch-correct a few off notes and it's almost undetectable.
Then they go extreme with the effect, creating the "warbling" effect that is best known from Cher's "Believe." In the podcast, they cover the misconception--which I shared--that "Believe" was recorded with a different device called a vocoder, which is enjoying a small resurgence among some electronic bands and was used to great effect by Neil Young on his 1982 album Trans. It's hard to tell the difference, but vocoders can be used for much more extremely distorted sounds--demonic robots on a rampage--while pitch-correction always sounds musical, if a little bit artificial.