"I've seen it used - the note pitches show up on a screen and fixing problems is about as difficult as fixing spelling errors in a word processor with a spell checker...

The effect is deliberately overdone on pop vocals everywhere, but when used carefully to fix minor pitch problems it often isn't noticeable."

I often wonder how much of a relative term "noticeable" is with Melodyne.

For instance, I've heard it used on a couple of recentish albums by various Bright Young Britfolk acts. Another good example would be the last Ron Sexsmith album.

I've no idea if a studio engineer would describe this as "subtle" or "unnoticeable" Melodyne, or not. It's a long way from the Cher vocoder sound, but it still sounds unnatural.