One of my Linux boxen is primarily used as a server and frequently just sits around without monitor, keyboard or mouse attached. While previously, it used to be connected to the network via ethernet, now that I've got the USB wifi adapter for my machines, it's even niftier and only requires power to get up and running.
One drawback to the above setup was that unlike my ethernet connection, my wifi connection was not being enabled until I logged in. The network-manager plasmoid was responsible for handling this and there appeared to be no option to get this happening prior to a login. A quick google turned up Wicd, an alternate network manager application which advertised that it could automatically connect during boot.
sudo apt-get install wicd and a couple of breezy configuration screens later, I was connected to my wifi network. A reboot also confirmed that the machine was logged on to my wifi network without requiring me to log in personally.
What's more, wicd's tray icon is a lot friendlier than the network-manager plasmoid :)