After iTunes 11.2 upgrade, big CPU and kernel memory usage

Question

The first time I opened iTunes 11.2 after the upgrade, I hit next. I then fought to open Podcasts settings because I had a feeling the delete listened to would be on (it was), then turned it off. It was very difficult to get the iTunes UI to respond. Eventually the whole machine was slowing down, so I had to kill it.
After a reboot, I started iTunes again. This time I didn't even get the UI to come up, just high CPU usage (75-90% by iTunes), and quickly-growing kernel_task memory (> 4-5GB, was around 2GB before starting iTunes).
I can't get the iTunes UI to come up anymore.
Repairing disk permissions didn't help.
I have over a hundred podcast subscriptions, and some of the subscriptions have hundreds of episodes downloaded. I don't want to delete any of that because some of it can't be redownloaded. (Not that I can delete anything right now, as I can't get the iTunes UI to come up!)
Has anyone else seen this?

Answer 1

Please read this whole message before doing anything.
This procedure is a test, not a solution. Don’t be disappointed when you find that nothing has changed after you complete it.
Step 1
The purpose of this step is to determine whether the problem is localized to your user account.
Enable guest logins* and log in as Guest. Don't use the Safari-only “Guest User” login created by “Find My Mac.”
While logged in as Guest, you won’t have access to any of your personal files or settings. Applications will behave as if you were running them for the first time. Don’t be alarmed by this; it’s normal. If you need any passwords or other personal data in order to complete the test, memorize, print, or write them down before you begin.
Test while logged in as Guest. Same problem?
After testing, log out of the guest account and, in your own account, disable it if you wish. Any files you created in the guest account will be deleted automatically when you log out of it.
*Note: If you’ve activated “Find My Mac” or FileVault, then you can’t enable the Guest account. The “Guest User” login created by “Find My Mac” is not the same. Create a new account in which to test, and delete it, including its home folder, after testing.
Step 2
The purpose of this step is to determine whether the problem is caused by third-party system modifications that load automatically at startup or login, by a peripheral device, by a font conflict, or by corruption of the file system or of certain system caches.
Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards, if applicable. Start up in safe mode and log in to the account with the problem. You must hold down the shift key twice: once when you turn on the computer, and again when you log in.
Note: If FileVault is enabled, or if a firmware password is set, or if the startup volume is a Fusion Drive or a software RAID, you can’t do this. Ask for further instructions.
Safe mode is much slower to start up and run than normal, with limited graphics performance, and some things won’t work at all, including sound output and Wi-Fi on certain models. The next normal startup may also be somewhat slow.
The login screen appears even if you usually log in automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.
Test while in safe mode. Same problem?
After testing, restart as usual (not in safe mode) and verify that you still have the problem. Post the results of Steps 1 and 2.