Unless you actually LIKE that goddamn worthless "Unity" interface, don't even bother updating. Unlike with 11.04, you will NOT be able to switch from that piece of shit to the normal desktop.
I honestly do not know what the fuck Ubuntu was thinking with this shit, I could see where it might be a good option on a tablet PC, but as a default on a desktop, Hell no.
Worse yet, I think Microsoft is actually copying this fucked up idea for Windows 8. Figures....they finally take an idea from Linux and its the worst thing possible.