Gotchas I ran into when trying to get MythTV working again:

1. The upgrade lost/removed the libqt3-mysql support from my computer. This resulted in the MythTV applications (frontend and backend) giving "unable to connect to database" errors. As the upgrade had also upgraded my MySQL install, I spent a good amount of time checking that the mythtv user still existed and had the proper permissions before I figured out it was a QT database library problem.
  apt-get install libqt3-mt-mysql fixed it.

2. LIRCD stopped receiving commands from my HDHomeRun receiver from SiliconDust. Turns out you have to change the LIRCD_ARGS="-d 5000" line in the /etc/lirc/hardware.conf file to LIRCD_ARGS="-H udp -d 5000".  After this, typing irw showed that LIRCD was now receiving the command codes as it was supposed to.

3. The module name for my D-Link GWL-G122 usb wifi-adaptor have changed, so I had to change entry in the /etc/modprobe.d/blacklist  file to reflect the new name(s) of: rt2x00usb and rt2500usb.

Related posts:

1. How to move a mythtv database from one machine to another
2. Installing core Microsoft fonts, Ubuntu (Gutsy/Feisty)