At first I have to say that the gnome system tools are very well intergrated in ubuntu and gives you the feeling that everything fits.
Anyway, the gnome network configuration is really bad. It is highly unclear how to manage profiles because you never know if you change an existing profile, make changes without any profile or create a new one! If you return to the configuration it is not even shown which profile is active.
Take a look at the IBM Connection Manager and you can see how this can be done. Maybe the configuration needs more modes here: One for networking without any profiles (e.g. Desktop PC) and one for multi-profile support (e.g. Notebooks).
Another point is the network monitor: If I have selected a profile where eth0 is not active it is useless that the network monitor show me that. I should show the next active network which is much more interesting..
Also have a look at 40+ Suggestions for Better Desktop which is right in many points IMHO.