Until a few minutes ago I was not really happy with the current configuration for (wireless) networking on my notebook. When I wanted to change to another (wireless) network (e.g. when I was not at home), I had to go to the network settings and change the network there. If I went to a new place, I had to use
iwlist scanning to find out which networks were available and then manually enter the essid to the form. Connecting to the network was then rather slow, sometimes it did not work (always switched back to another network that was not available at the current place) and I had to reboot. Thanks to Clem who told me about the NetworkManager this is now over. Originally it is a gnome-tool but it works perfectly on my Ubuntu with XFCE.
I installed NetworkManager by the command
sudo apt-get install network-manager, commented out (with #) all lines except those with
lo in /etc/network/interfaces and rebooted. The first time I had to start the NetworkManager using
nm-applet, since then a small applet has been in my xfce-panel. Similar to windows I can click on it to display available networks. By clicking on an entry, I can connect to the corresponding network (and enter the network key).