Although Confluence the default XBMC is nice, there are far more beautiful skins for XBMC. Aeon is one of the best:

To install this very spiffy theme in Ubuntu, you first have to install Git for accessing the repository:

sudo apt-get install git-core

Go to your XBMC addons directory and install Aeon65:

cd ~/.xbmc/addons
git clone git://github.com/pix/aeon.git skin.aeon65

After this you can select Aeon in XBMC