I am having the same issue as the others, and I will list the steps I have taken.
First my setup: OS X Mavericks (10.9.1), Late 2012 Mac Mini 2.6GHz i7 16GB (3rd Party Memory) 1TB Fusion Drive (Factory/Apple installed) Music Files stored on 500GB WD Passport External Drive, iTunes library stored on internal 1TB Fusion drive. Running iTunes 11.0.4 11.1, 11.1.2, 11.1.3 (I have had the same issues with all 4 releases)
The problems began when I attempted to add a ripped movie file (legitimately purchased dvd's that i would like to convert to .mp4 or .m4v files to be used/streamed to Apple TV since i no longer own a DVD player) to my itunes library. The file would show copying 1 of 1 to itunes library, then would freeze at some point, becoming completely unresponsive. Leaving itunes running would not solve the issue. Force quitting itunes would cause me to be unable to reopen itunes. I would also not be able to restart my computer through soft-reset (file, shut down or restart) methods. Instead I would be given a gray screen, and the computer would just hang. I would also not be able to relaunch finder. The relaunch would hang. So I am forced to hard reset my Mac mini (holding down the power button on the unit to power down the unit, then hitting power again to power it up. Itunes would also freeze and become entirely unresponsive with no recovery when i selected all my movies files and tried to change their sorting from "home videos" to "movies"
Things I have tried without success:
reinstalling mavericks over existing OS using backed up itunes library
reinstalling mavericks over existing OS using newly built itunes library
Clean install of mavericks and backed up/restored itunes library (post migration assistant to recover apps only)
Clean install of mavericks and newly built itunes library (post migration assistant to recover apps only)
Clean install of mavericks and backed up/restored itunes library (pre migration assistant)
Clean install of mavericks and newly built itunes library (pre migration assistant)
downgrading OS to Mountain lion 10.8.5 with newly built itunes library
downgrading OS to Mountain lion 10.8.5 with backed up/restored itunes library
tried moving all media files to internal fusion hard drive
deleted itunes entirely using terminal, and reinstalled version 11.1 from an exisiting time machine backup
if you're losing count, that's 6 clean installs counting the downgrade to 10.8.5 9 (each time using disk utility to erase the hard drive then installing the new OS on top of the empty drive).
additionally i have:
run memory test overnight using memtest86 with no errors.
verified and repaired disk permissions on both my internal hard drive and the external drive the music/video files are located on
run apple's hardware diagnostic test multiple times showing no failures
disconnected all other drives/storage/etc and connected only the passport drive directly to the computer.
i am also unable to boot into safe mode (reboot and hold shift until the progress bar shows, release shift, a few moments later computer restarts on it's own and boots in normal mode)
i've also documented my issues in the following thread on macrumors:
http://forums.macrumors.com/showthread.php?t=1687810&page=2
i have a genius appointment tomorrow, but not expecting much. i will however be demanding a fix, since i spent $1500 on my Mac mini, and now it's virtually useless as a media server for Apple TV, which is part of my intent in purchasing it.