UPDATE - My video guide is here: http://www.youtube.com/watch?v=TusVGE702rw
I just saw that XBMC 12.1 was released today. While I do not necessarily use all the features they improved, I wanted to give the new Audio DB plugin a try so I decided to upgrade.
I went from 12.0 to 12.1 by upgrading over the Internet instead of doing a fresh install. The guys at XBMC.org have posted a guide on their wiki, however, after following it, I got a Linux login screen instead of XBMC. Turns out their wiki instructions are missing a command.
Here’s what you gotta do to upgrade: If you are doing this remotely (via ssh) look up the IP address of the computer you are connecting to (you can do this under system -> hardware), or go to the a VTY by hitting CTRL+ALT+F1 on your keyboard.
Once you are at the command line I used these commands to upgrade:
sudo add-apt-repository ppa:team-xbmc/ppa
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install xbmc xbmc.bin
You may be asked if you want to continue, or install/upgrade packages. If you are asked, either hit enter to continue or Y to continue depending on the prompt.
Once you reboot, cross your fingers and your toes, and you should be able to get right back into XBMC. If you got a login screen after following the steps on the official wiki article, go back to a command prompt and also run “sudo apt-get upgrade” then reboot.
I did a quick take, and 12.1 can work with 12.0 using the same MySQL backend, and the YouTube plugin works as well. I did not have a chance to test much else!
Good luck, and let me know if you have any questions!
P.S. If you are interested in what 12.1 fixes, read the official brief here: http://xbmc.org/natethomas/2013/03/18/xbmc-12-1-now-even-better/