I updated iTunes from 10.7 to 11 today on my Windows 8 system and wasted 4 hours trying to make it work before downgrading back to 10.7.
My system would partially hang during startup resulting in most startup apps not loading and the desktop becoming very unstable.
I suspect a conflict between iTunes and one of DropBox, Google Drive, Air Video Server, or FileZilla server.
To make matters worse, iTunes 11's user interface is a big step backwards in my opinion.
Be aware that to downgrade you need to restore a backup of your library so you would be very wise to make a backup before upgrading.
If anyone experiences similar problems and finds a solution a post here would be appreciated.