Every time

Every time you connect to a wireless network Windows saves the key for later use, you can't view the keys normally so that's where an external program like WirelessKeyView comes in. This portable app will let you see every key on your PC that has been used to connect to a wireless network, handy if you want to store in a text file for later use.
Just remember this is not a cracking tool of any kind, WirelessKeyView will only display the keys to wireless networks you are currently connected or connected in the pass. Definitely worth a look if you use wireless networks a lot. Available for all Windows versions.