If I want to Add the Medibuntu Repository (and any other repo's for that matter), I have to go to the terminal and add something like following lines
sudo wget http://www.medibuntu.org/sources.list.d/intrepid.list --output-document=/etc/apt/sources.list.d/medibuntu.list && sudo apt-get update && sudo apt-get install medibuntu-keyring && sudo apt-get update
(Or the repository of your choice)
It would be nice, in the add/remove there was option to run this command for you, adding the repository into the /etc/apt/sources.list.d/medibuntu
Also there could be others like wines repo's etc - which you have to drop in the terminal to do normally, but if there was a GUI it would be ALOT easier (a new users would be more comfortable with it as well)
======
After the install it would be nice, if there was a option of seeing what new application are available after adding new source list to your repository
(Maybe a extra box in the add / remove)
Mediaubuntu - listing thing like google earth, skype etc Wines - stable version and development version etc
This give new users a easy way to install extra stuff that doesn't come by default with ubuntu