Since X3's release, I have been one of those people you don't want to chime in. Melodyne has worked brilliantly, and is an incredible piece of software, especially with the upgrade to editor.
Until yesterday.
I had done some vocal edits the night before, mainly as special effects, but when I opened X3 the next day, the vocal tracks played back unedited. The clips still showed as region fx clips. When I launched Melodyne it showed the audio all in one line, as if it was using the percussion algorithm. Nothing worked in Melodyne, no buttons, menu options, etc. Over an hour of editing lost.
I had a student coming round at any minute to work on this track, and had to madly rush to get it re-edited. In my panic I neglected to check my other versions of the project (I have versioning ticked) to see if they still worked. I will have a look later.
I'm sure I have seen other threads about this saving issue, but didn't find them just now.
I also think this may have happened to me before, in a much smaller way, but I had put it down to pilot error.
I'm not sure if it has crashed X3 - I've had a few crashes (far fewer than on most new versions of Sonar), but don't think they were Melodyne related, but I suppose it's possible.