If I take a backup of my phone in iTunes while it's jailbroken, and then revirginize it, and then restore the backup I made, will it fail because I'm trying to put a jailbroken backup onto a virgin phone?
^It did for me because I went 1.1.4 to 2.1 and backed up with a lot of third-party stuff installed, but I managed to fix it while it was in the spinning wheel of death by rejailbreaking and just editing a few different plists at the right time in iPhoneBrowser, despite the phone being non-functional.
Also, that was an extreme case; in other cases of a corrupt backup, you can usually simply delete something (don't remember exactly what) in SSH and it will be fine.
You can look for a thread by me from when I was having trouble with it (and was incredibly upset) for more insight.
Well, that seems to be a specific problem that you were having. Does anyone know if restoring jailbroken backups on a virgin phone generally breaks? It would suck to lose a whole lot of texts and contacts because of a corrupt backup.