I could have sworn I saw a thread recently about an app that helps to manage multiple interfaces, but I can't seem to find it (maybe I'm just crazy).
Anyway, a somewhat easy way to manage this is to create multiple interfaces files (/etc/network/), one for each network you use. For example, I have interfaces.home, interfaces.wellenreiter, interfaces.coffee. When I want to change the network, I just rename the correct file to from say 'interfaces.home' to just 'interfaces', then go to console and type 'ifup wlan0'. (You may need to do 'ifdown wlan0' first if you're card is still on (from the previous network).
You can either create the seperate files manually, or just use the network app to create one, then copy/rename the file and use the network app to create the next one, and so on.
Does this make sense?
good luck