It looks like there's an interesting bug in the current version of Adobe Air for Linux which, if you install it, can affect the Ubuntu Add/Remove Applications programme.
So, if you find that after installing Air, you have no applications at all listed in Add/Remove Apps, do this:
In terminal, type sudo update-app-install
If that doesn't work, reinstall the Add/Remove Apps application:
sudo apt-get –reinstall install gnome-app-install
This should do the trick. According to Rohit Kewlani of the Adobe Air team (posting in the above thread), this should be fixed in an upcoming Air release.