I toyed with an earlier incarnation of Melodyne before, and while it was a nice looking, it really did nothing more than what my TC Helicon Voiceworks can do for me in both a studio and live session. Hardware Pitch Correction with extended harmonies > Software ...
I live my dream playing around pretending I'm Hansi and singing Mirror Mirror to myself!
So anyway, onto their new abilities, I'm indifferent. While I am the shittiest guitar player on this side of the Delta, it just feels too much like cheating to edit anything on such a level as that. However, say I were to just fuck up a few notes on a lead, currently, for a clean sounding edit, you have to essentially re-record that whole section. Any pitch alterations make it sound awful, unless you're a extremely familiar and talented with your tools (not me), and the ability to quickly fix a little fuck up without it sounding out of place will be something nice for the poor guys in charge of mixing and mastering.