What can I expect to accomplish with Melodyne Editor

The incentive to upgrade to X3 has certainly been increased with the option to upgrade to Melodyne Editor for a juicy price.
 
Yes, a year back I saw a youtube video of the opening piano part to Let It BE changed in an unimaginable way - I was stunned - I thought such a thing was not technically possible.
 
I undertstand that the source material has to be homogenous, but I'd like to understand what I might be able to do with it and what some of it's limitations might be.
 
Will I be able to take an Acid loop of some Wurli / Rhodes / Hammond / Clav performance, and alter some notes to change chords?
 
Will I be able to take an undistorted guitar performance of mine and be able to extract MIDI notes from it, so I don't have to by a guitar synth?
 
Will I be able to adjust / tune existing vocal harmonies?
 
I understand that extracting individual drum parts from a full drum audio performance is not really possible, although somehow it can be done in Live.
 
Is there anything else which Editor will allow me to do which I am overlooking?
 
Thanks guys (and gals).

The polyphonic editing is quite amazing, but in terms of the audio to MIDI conversion, expect to put some effort into preparing the audio in Melodyne first. You're going to have to go through it and check all of the notes because it will confuse some overtones with notes and has trouble recognizing notes an octave apart in a chord etc....usually it's just a case of toggling Melodyne blobs on or off though. 
 
And when playing guitar to be converted to MIDI, you have to make sure of a number of things. First, that the recording is as clean as possible (the more overtones e.g. distortion, the more chance of inaccuracy). Then, you have to think about your playing technique a lot. For instance, imagine that you're looking to create some straight synth chords from guitar but you have a natural tendency to arpeggiate chords a little when plucking them. You have to think about playing all notes cleanly and simultaneously, unless you want a lot of editing work either in Melodyne or the PRV. And you may find that the velocities of the notes in your chord are all over the place when you convert them to MIDI. Again, you may have a lot of editing to do. 
 
You basically have to pay a lot more attention to your guitar technique then when you would when recording a guitar guitar part. Loose technique that adds character to a guitar part is almost guaranteed to sound terrible when converted to MIDI and played through a synth. 
 
Basically it's not the guitar to MIDI nirvana that I thought it was going to be, but that's just down to me having unrealistic expectations I guess. When I think about what it does and how it's allowed me to get MIDI parts down that I would never have even attempted before, it's an extremely useful tool. And I'm finding that my guitar voicings sound great on keyboard 

+1 to everything above - the existing videos and Celemony content are why I upgraded to Editor last year.
 
Aside from that and to answer the OP: I have done every one of those things.   Most turned out well, and those that didn't were still passable in the mix.  It really does depend on the source material so this is absoutely a case where YMMV.