I tried to use saliency-based approaches but they don't really work that well for non artistic photos. For example, this image would have edges everywhere but next to the faces.
If you have some time, I would be interested in seeing the results of your approach in my example images.
 - https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-snc6/p206x...
 - http://blog.vjeux.com/wp-content/uploads/2012/10/cropping.ht...
edit: I even think you are using a similar method.
Seems to be a similar solution using PHP and ImageMagick.