At long last, Spotify has launched the web extension it introduced last year. Unfortunately, it left a gaping security vulnerability that leaves the songs wide-open to download with a simple Chrome extension. UPDATED.
According to the developer of Downloadify, Spotify neglected to encrypt the Mp3s coming across the web to your browser to your ears. They even suggest a potential fix for the problem. Until the problem is fixed, Downloadify will let you pull down an MP3 of any track just by double-clicking it.
It's definitely illegal. Do with this knowledge what you will. YOU HAVE BEEN WARNED.
Update: It appears Downloadify has been pulled from the the Chrome store. If it's already installed on your computer (or you can find another way to get it) it still works.
Update 2: Here's a very special message from the man supposedly behind Downloadify:
— Robin Aldenhoven (@rAldenhoven) May 8, 2013