I created Multichannel Forensics as a way of simplifying some of the more technical aspects in biological and ecological modeling.
Every so often, a gifted marketing individual applies the concepts of biological and ecological modeling to practical marketing issues.
In this case, Andrew Chen shows how a topic called "carrying capacity" (i.e. the upper limit in growth of your business) and customer retention are applied to applications in Facebook.
If you like math, pay close attention to the equations used in his post.