Detect when user plugs in a network cable

In Ubuntu, if while the computer was booting, the router was off, and after the boot is turned on, the networking won't work, and the user will have to restart the computer to make it work. (or issue a /etc/init.d/networking restart, but the typical end user would never know that)

I suggest to make some kind of sentinel that in times to times, check if a network is available and connect to it.