This is the Editor version...I don't use the polyphonic mode much, but I learned its power last night.
 
I was recording a slide guitar part where the slide had to move rapidly over five frets. On one take I hit the timing perfectly, but the slide was angled slightly so the upper and lower notes were out of tune.
 
I opened the clip in Melodyne, turned pitch correction up to max, and...ohmigod! It became perfectly in tune, while preserving the slide itself and the vibrato. Pretty amazing.

I don't know how I lived without Melodyne.  I'd rather give up cell phones.
 
Of course, the disadvantage is that we have trained the general public to expect dead-on pitch and when they hear a singer that's a few cents off, they know something's wrong, even if they can't explain what.

I really need to learn how to use it properly! My experience has been a bit frustrating, but I attribute that to not putting the required time into learning it.

it works great on female vocals to fake another harmony. 

That's a great use for the polyphonic mode and similar to the way I've used it to fix guitar chords. I also love the ability to delete offending notes or noises.

konradh
.... a few cents off, they know something's wrong, even if they can't explain what.

I've been a few cents off my entire life....Oh wait!  You were talking about singers. 
 
I've been using Melodyne since Uno came out and it worked great for tuning vocals.  Since RMA arrived it's a whole new world.
 
Paul

Vocals tuners are great help ,you record less takes,but I have to say some good singers with nice sounding voices I would never use anything with there voices it kills there natural vibrato.
Peace

Hmm I tried to use Editor to fix a guitar part that was recorded with a couple of the strings slightly out of tune. It did this weird smeary thing with the transients. 

sharke
Hmm I tried to use Editor to fix a guitar part that was recorded with a couple of the strings slightly out of tune. It did this weird smeary thing with the transients. 

Well, there weren't any real transients. I was doing greasy distorted slide, not Nestor Ausqui on nylon-string classical guitar...
 
Mainly it just blew me away that it could fix an "off" slide chord so easily, without killing the slide itself or the vibrato. Maybe I'm just easily amused, but that would HAVE to have been a retake before Melodyne came on the scene. 

maltastudio
Vocals tuners are great help ,you record less takes,but I have to say some good singers with nice sounding voices I would never use anything with there voices it kills there natural vibrato.
Peace

I've found that Melodyne handles natural vibrato really well and actually repairing pitch doesn't really affect it. In fact I would say that that is one of the criticisms of Melodyne (especially compared to V-Vocal) - it doesn't allow you to create your own vibrato or alter the recorded one very freely. You can only increase or decrease the naturally present vibrato.