I have been struggling to get to 12.04 for one of my three systems supporting Mythtv.
There have been multiple false starts and not working functionality.
Furthermore, Unity severely upsets my working style.
Is there a way to do this?
Note: I have switched to Xubuntu from Ubuntu. Originally I thought it was for older, less robust hardware but found it's avoidance of the "advanced" Ubuntu's complexity a blessing and a truly useful desktop for me.
Update: I should have noted that this works for Ubuntu and Xubuntu, Xubuntu just being a plus. I removed Unity after final Xubuntu upgrade.
Note: I upgraded a very simple 10.10 Ubuntu dedicated to an mythtv client to 12.04 without any problems. My big workstation for 10.10 mythtv support was a different story...
The one anomaly not fixed was the 2nd monitor screen1 not being drawn properly, but with Xubuntu I at least get partial functionality.
How I did it (over weeks and many, many false starts)...
If upgrade to 11.04 fails (mine did), you may have to restore the MBR grub, hence the burned boot-repair disc.
I found that during download of the release upgrade packages the download would hang. If still downloading, it can be stopped and software sources used to find another server.
I found best practice to switch to the main Ubuntu server when not able to complete download, often slow but sure.
I am blessed with reliable high speed INTERNET access, but still had download problems.
During the upgrades, I found duplicated sources (usually "Canonical partners"...) which I reduce to a single one using software-sources.
I did my upgrades with a dual boot 10.04 (helpful when backing up and restoring but troublesome with grub2. If you use live CD, make sure you have one for each release, 10.10, 11.04, 11.10 and 12.04.
Each upgrade step took a minimum of two hours, and the upgrades stops when it asked you a question, so prepared to be bored.
The 11.10 to 12.04 upgrade has a bug wherein the upgrade ask you a question but you can only see it if you have "terminal" opened, so open it, good idea far all upgrades.
Make sure after each upgrade you back up well, because you may have to stay there awaiting things to be fixed. Good idea to keep prior backups until the desired end result is reached.
In conclusion: If you are trying this and broach at a problem, ask a question on askubuntu and here leave a comment pointing to the question. I will endeavor to answer. And good luck.
My 12.04 Xubuntu workspace (open in a new tab/window for full size)...