Went and installed the latest nightly for my i9305T. What I didn’t notice was the nightly is for CyanogenMod 10.2, which is based on Android 4.3 . Since the version of Google Apps I had installed was for Android 4.2, it went badly.
Anyway, after a lot of sweating, I got the phone all back and running again with no lost data. The take-home there is, if you install the recent nightlies (eg http://get.cm/?device=i9305 ) where they are CM 10.2, you have to also install the latest Google Apps (eg http://goo.im/gapps/gapps-jb-20130813-signed.zip ) as well.
The ‘right’ way to do this now would be to download the CM package and the GApps packages, put them on your external SD card, then boot into ClockworkMod, and install the CM zip, then the GApps zip. Reboot the phone and you should be golden.
Take a backup first using ClockworkMod.