I decided to downgrade my iTunes from 11 to 10.7 for a number of reasons, top most was the fact the the new UI drives me barmy!
I followed the great instructions at http://arstechnica.com/apple/2013/03/how-to-downgrade-from-itunes-11-to-version-10-7-on-your-mac/ and found that I couldn't open my iTunes library after the upgrade.
Since I didn't make a library backup before the iTunes 11 upgrade I
thought I would be stuck, but to my surprise I found a Previous iTunes Libraries folder in my ~/Music/iTunes
Restoring was as easy as taking my swapping iTunes Library.itl with
the file in the Previous iTunes Libraries folder from December and
everything worked fine...
One thing I noticed was that my new iTunes purchases didn't show, but this was a minor inconvenience. Now I have the old iTunes back and I'm happy… for now...