I am a long time Mythbuntu user. It's fantastic, and makes setting up MythTV pretty darn easy.
I recently upgraded from a really old Mythbuntu release to 12.04 in order to upgrade to MythTV 0.26. In general, it went well, after working out a few issues.
The one thing that has persisted, which is really annoying in a 10-foot interface typically driven by a remote control, is the Update Manager behavior.
It seems like every time I power on my projector, I am greeted with a dialog box for the Update Manager. It, of course, has the GUI focus, so I cannot use MythTV until I go get my laptop and use VNC to connect in and close the dialog box.
I first set update checking to the least frequent interval, but it still seemed to check more often. I set it to operate in the background so it wouldn't interrupt MythTV, but it still does. I have tried several other things, but still get the annoying dialogs. Yesterday, I turned off Update Manager update checks. Today, I was greeted with a dialog saying "You must check for updates manually".
Come on! This is ridiculous. This behavior may be acceptable on a PC where you're already sitting in front of the keyboard and mouse to operate the system. But, in a Home Theater this is not acceptable.
To top it all off, the VNC server in 12.04 doesn't seem to like connections from my Mac, either using the Screens app or the Apple Remote Desktop viewer. It constantly disconnects (crashes?) making it even more difficult to get rid of the update manager messages.