Before the Ubuntu upgrade

Before upgrading, check if all your non-Ubuntu repository applications are available. For XBMC you can check the XBMC roadmap

After the Ubuntu upgrade

We need to reinstall all applications, which are not in the Ubuntu repository. They were cleaned up automatically.

Installing XBMC

See here for all instructions: Installing XBMC on Ubuntu

Installing DropBox

Download the debian package here: Linux

Just open the downloaded Debian package (Ubuntu x86 .deb).