I'm guessing I'm in the minority, but I have mixed feelings about Melodyne. I love it conceptually, especially the polyphonic algorithm (how mind-blowing is that?), but, when using it for pitch correction, it's rare that the results don't sound phasey to me and lack the high end the definition of the original clip.
It may be that I have more to learn about how to use it effectively. I don't doubt that, but, so far, I've been able to get results with better fidelity from AutoTune in graphical mode. As an aside, I think a lot of folks have a negative view of AutoTune, because of how it's been (over) used as an effect and because of how unnatural it sounds when used in that manner. Additionally, I think a lot of people are unaware that AutoTune has a non-auto mode.
One of the things I have been happily using Melodyne for recently is working out vocal harmonies and then singing along to the retuned clips when I record those parts. This way I can concentrate on matching the timing and feel, but not get distracted by the notes of the original melody. Better singers probably have no issue with this, but my voice often slips back into singing in unison with the melody, if that's the part I'm listening to when recording the harmony.
Another thing I've been using it for lately is the amplitude tool. This works great for leveling out dynamic performances without the side effects of compression and without introducing the phasey artifacts I mentioned above that result from using it for pitch correction.
All in all, I think Melodyne is an amazing product that does a lot (I haven't even touched the timing tool yet). I do hope, however, that in subsequent versions they will improve the audio fidelity of the pitch correction algorithm.
Cheers!