A post on one of the support forums offered (this windows user at least) a solution to the botched iTunes 11.1.4 upgrade. Basically it says to remove all Apple software from the Control Panel Programs list with "uninstall" and delete all the following folders:
- C:\Program Files\Bonjour
- C:\Program Files\Common Files\Apple
- C:\Program Files\iTunes
- C:\Program Files\iPod
- C:\Program Files\QuickTime
You can leave your media folder alone. After uninstalling all Apple software, deleting the above folders and rebooting the PC, it has been recommended to install Quicktime first before installing the new iTunes version. With a bit of luck your iTunes will install and run succesfully (it did for me). Though somehow with this version of iTunes, there are some issues when playing back mp4 video files. Sometimes the picture would hang even though the audio is still playing. The same video played in VLC plays without any fault.
Update: Apple just released a support document to succesfully install itunes