20K empty playlists later, iTunes syncing is completely broken

iTunes has been acting worse and worse for the past month.

It started with an iTunes Match problem...

I created a playlist on my iPod Touch when I wasn't connected to a network. When I did connect to a network, iTunes Match began to populate more than 20k empty playlists and brought iTunes, my iPod, and my iPhone to a crawl. Every device that had iTunes Match enabled (MacBook Pro, iPhone, and iPod Touch) had all of these empty playlists on them, and iTunes Match kept populating these playlists until I turned it off on each device.

I tried to fix that problem and asked for help on these forums, but couldn't find a solution. I eventually just gave up for the time being and turned iTunes Match off on each device.

Since then, I am unable to sync or drag music, movies, podcasts, or anything to my iPhone or iPod Touch. I have wireless syncing enabled on each iDevice, but iTunes only shows the iPod in the sidebar. Despite that, whether plugged in or not, iTunes will not move music to these devices.

With the iPod, I can drag music to the device, but it never actually moves it. For instance, I tried to move a song to the iPod while plugged in, and it looked like it was working (spinning wheel in the status bar on the iPod, spinning wheel in iTunes) for a few seconds, then it looked like it was finished. When I go to look for the song on my iPod, it isn't there. When I look at the iPod's library in iTunes, the song is there, but greyed out as if it's still syncing. I can let the iPod sit there, plugged in, for an hour and nothing ever happens.

As for the iPhone...

I can connect it to my MBP and it will show up in iTunes, but it won't let me drag anything to it. Instead of showing the little music icon with the plus sign on it, the files I try to drag to it simply fly back to where they were, as if the iPhone is something that can't be synced.
I have tried everything I can think of. Everything is updated to the latest version (OSX 10.7.3, iTunes 10.5.3, iOS 5.0.1). I've tried restoring the iPhone and iPod, I've tried rebuilding my iTunes library, I've tried a clean install of iTunes, I've repaired disk permissions, I've tried using Time Machine to go back to when iTunes worked, and have even tried reinstalling Lion via Lion Recovery.
Nothing is working.
I know this is a lengthy post, but I wanted to explore every solution before I cart everything up to the genius bar.
Does anyone have any idea what may be wrong?

I have an odd notion that perhaps I have a bad file somewhere in iTunes and might even know where it is. It was an album that I tried to put on the first playlist that caused all this trouble, and I downloaded it (legally, I might add...from the label) right before all this happened. Maybe that's it?