Robbie Ferguson of www.Category5.tv has written a great script that automatically upgrades your new installation of Ubuntu 9.04 (or older versions) with multimedia codecs, flashplayer, Skype, fonts, and other things to make Ubuntu play nicer with the wide world out there. You can find it here.
1) Download the script to your desktop.
2) Right-click on the desktop icon, select “properties”, then select the “permissions” tab, and check the box to allow executing the file as a program.
3) Open up a terminal (Konsole, or whatever your favorite is), and type cd /home/[yourusername]/Desktop/
and press enter.
4) Type ./perfectbuntu
Now you will be asked for your password, and then for your preferences as to which things you would like to have installed. Type y for yes, or n for no, and press enter.
This is where Ubuntu’s apt-get takes over, and fetches and installs the requested software, and bingo! You should be all set for YouTube, mp3’s or whatever.