The very first thing I do with a new laptop installation of Gnu/Linux is to install Network Manager (sudo aptitude install network-manager-gnome). Eventhough I have met people who have claimed to hate it to death, I still consider it to be the best invention since the invention of sliced bread!
However, something very peculiar happens if you install it after you’ve already used your laptop to access a.. uhh… access point: the little Network Manager applet won’t detect the wireless device!
The solution, though not very intuitive, is to edit the network interfaces file and restart the program.
sudo vim /etc/network/interfaces
Search for lines related to your wireless device and remove them as shown below (my actual file):
wireless-essid Mordor wireless-key theonetobindthemall
After you save the file, disable and re-enable the Network Manager applet by right-clicking on it, and that is it! ;)