I am using Ubuntu 10.10 Maverick, and I have this problem where the NetworkManager just quits randomly causing the internet connection to be broken. The only way to get it back is to log-off or restart the computer. This is very annoying as you have to close all the work you are doing and log-off or restart the computer.
The Networkmanager icon in the panel is not visible anymore when it quits as shown in the screenshot here.

However the hardware icon for the wireless is still on which shows that this is a software problem.
Has anyone else experienced this problem? Is there a command or something to restart the networkmanager applet when it quits?