The first time you start Ubuntu, after installation, show a Post-installation assistant, allows step by step, for example, create new users, automatically detect and configure new hardware (printers, scanners, webcams, etc), ask to the user to activate new repositories (medibuntu.org), option to disable services that are not needed by the user, option to turn on full support for the selected language, third party applications (audio and video codecs, flash, extra fonts, etc) and an option to change the look (change the display settings, wallpaper, gnome theme directly).
All in a centralized assistant, immediately after installation.
There is a similar idea at
http://brainstorm.ubuntu.com/idea/11850/
but my idea is oriented to the system configuration , not only add new packages from internet.