Mac power users have known about this feature for over a decade. Theres also a pretty powerful wifi diagnostic tool in the coreservices folder, if you're going to be digging around in there anyway.
In Mavericks at least, you can hold Option and click on the Wifi icon in the menu bar to get an "Open Wireless Diagnostics" option in the menu. And you're right -- it's pretty handy when you're surrounded by college apartments that all have their own routers.
Are you talking about this command-line tool ? /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport . Great to scan wifi networks and find unused channels.
