Model for Viral Growth

One of the things in my mind is to create a sufficiently accurate model to predict viral growth - While digging, I came across this very interesting blog post
http://lsvp.wordpress.com/2008/03/10/an-excellent-excel-model-of-viral-growth/
with a link here:
http://andrewchen.typepad.com/andrew_chens_blog/2008/03/facebook-viral.html?cid=106420002#comment-106420002

Some others
http://www.insidefacebook.com/2007/07/17/predicting-growth-with-appaholic/
http://www.skelliewag.org/the-butterfly-growth-model-224.htm