Gnome does not seem to have the ability for the user to tell it which network to prefer when more than one wireless network is available.  

In a way that's fine, since a UI for defining priorities would probably rarely be used and it would be a lot of visual clutter, but it still can be annoying to have it constantly auto-connect to the wrong network time and again.

It would be nice if gnome could tell, based upon the available networks, which wifi network the user prefers and maintain an internal network priority based on what the user selects.  So if SSIDs "attwifi" and "MyRouter" are both visible, when the user selects "MyRouter", the system should place "MyRouter" just above "attwifi" in the list of networks to automatically connect to.