NB! The bitly link in the deck DOES NOT WORK, please use this one: http://bit.ly/1JTymzd
This is the presentation I gave at Slush 2013 in Helsinki, Finland. It describes two methods for modeling Lifetime Customer Value (LTV) in Excel. Linked within the presentation is a spreadsheet exemplifying both methods against 100k rows of fake user data that I generated with a Python script to "look" real (although they probably don't).