A 'small, incremental change' over RC2
As the road to a stable CyanogenMod 10.1.0 release continues, the CM team has today started pushing out RC (release candidate) 3 builds for phones, tablets and other devices. If you're running any earlier build, you'll want to update via the get.cm download hub or CM updater app.
A Google+ post by the team reveals that it's a "small, incremental change" from the previous RC2 build, with fixes for issues including camcorder preview bugs, launcher icon alignment in tablets, disappearing widgets, along with a bunch of translation updates.
CM 10.1 RC3 is available for some 37 devices at the time of writing, so your best bet is to hit up the source link and check the list for your model's codename.