After re-installing OSX, AppleTV and iPhone don't recognize iTunes library anymore?

This is so annoying and the reason I so hate DRM.

Obviously, the last two Apple updates hosed up quite a bit, as now a whole lot of permissions are wrong, and Disk Utility can’t repair them. Plenty of it on the forums.

Me thinks I’m all smart and smug, re-installed Leopard (clean install).

Lo’ and behold, despite having everything set up exactly the same as before, AppleTV and iPhone don’t want to sync anymore, because they think this is a different computer, despite the iTunes Store recognizing the machine when I clicked “Authorize this computer”. Meaning, I got the “This machine is already authorized” message.

Now I have no way of “rescuing” my Apps installed on the iPhone, and syncing 250GB to my AppleTV will take days.

Isn’t there anyway to make this stupid thing see that this is exactly the same computer and library?