Just got the latest linux-headers-3.8.0-18 update. After a restart Grub launches, if I choose Ubuntu (its either that or a memory test) I get a screen of jumbled text and nothing else happens. Do a hard shutdown, grub launches again and use the advanced options to pick the previous kernel and everything back to normal.
Using the Nvidia 310 updates repo.
At least they are being consistent this cycle
UPDATE - Removing the Nvidia repo and using the default Xorg graphics lets the system boot up normally.
UPDATE - Bug #1169325 reported. Reported against the nvidia repo, but maybe it should be the kernel? There was also a 310-updates update.