I have updated to Ubuntu 12.04 for a few days, which worked out of the box and until now I just have found a few smaller problems afterwards which I describe here.
After the upgrade the sidebar does not hide automatically anymore. With 12.04 you can only choose between always showing the sidebar and autohide. The default is “Ever” which means showing it all the time. To switch it to “Autohide” start the CompizConfigSettingsManager (ccsm), find the “Unity Plugin” and switch “Hide Launcher” to “Autohide”. To install ccsm type “sudo apt-get install compizconfig-settings-manager”.
nothing else after a first glance but expecting more
to be continued…