You're right that the old trick of double-clicking on a network entry in your Networks system preference no longer works in the latest generation of Mac OS X, 10.7 Lion. I expect that it'll also be true in 10.8, so it's time to learn the new, fancier way to recover a wifi password.

As with the original approach, this only works if you already have the password to the desired network stored on your computer. If you don't know it, you won't be able to recover it. I know, sounds obvious, but you'd be surprised at the email and questions I get, the requests to point people to hacking tools, etc.

The new place to recover the wifi password is in an Apple utility called Keychain Access, and you can find it -- ingeniously -- in the "Utilities" folder within your "Applications" folder.

Launch it and here's what you'll see:

Use the built-in search function to enter the ssid or name of the wireless network whose password you want to recover. I'll recover the password for a local café called Tod's by searching for "Tod". The results:

Clicking on the "i" info button on the bottom of the page brings up a full Keychain record for Tod's:

Now all you need to do is check the box adjacent to "Show password" (though it's a bit confusing that the field adjacent to that is blank. Don't worry, Keychain has the data stored, it's just not showing it yet. Bit of a UI gaffe, but you'll see, it'll show up!)

Right. For security reasons you'll need to enter your Mac administrative password. Do so correctly and suddenly that blank text field has the Tod's network password:

And that's how you recover a lost wifi password on Mac OS X 10.7 Lion. Not quite as straightforward as in earlier versions of Mac OS X, but now you know how to do it, you'll realize that there's quite a bit of password information in Keychain...