Marc Charbonneau

From TidBITS Networking:

Leopard includes more information about Wi-Fi networks in the vicinity of your computer than meets the eye. Mac OS X 10.5 updates the AirPort menu in the system menu bar after you select, which is a neat feature and provides more accurate results. It also shows a lock icon next to networks protected by some form of encryption. But you can extract more information by holding down the Option key while selecting the menu.

Neat trick, although it would be more useful if it showed details for all the networks in range, instead of just the connected network.