this is a feature request, I guess.
Most mac apps allow you to swipe left on your trackpad or magic mouse to go back (or swipe right to go forward).
Spotify doesn't do this.
Version 0.9.6.72.ge329c074 on OSX 10.9 on a retina macbook pro.
Also, I wasn't able to select the text of the Version number from the "about spotify" dialog box. With a version number as long as this one it would be nice.