I've upgraded to Raring last night. The upgrade itself went okay, no errors. But when I rebooted the computer afterwards and logged in to my Unity session, all I could see was the Desktop background (together with Desktop icons), and no Unity interface. The Super button shortcut wasn't showing the Dash, there was no top panel etc. Please see the screenshot.
As a hint, I'm suspecting it's got something to do with my switchable graphics. I'm running Ubuntu on Acer Aspire AS5830TG with nVidia GT540M and an Intel integrated card. In 12.10 I was using Bumblebee to manage the graphic card switching. During the upgrade I saw something related to nvidia had to be uninstalled, but didn't pay much attention to it. I can't be sure if it has anything to do with my problem though.
What could possibly go wrong?