Isn't that an argument for assessment on a campaign basis? I'm still wrapping my head around his calculations. It looked like he included the cost of the ads prior to the reporting window in his multi-touch model. That's a fair way of measuring the true cost of user acquisition, but if the ads you are paying for today won't pay dividends until you're out of the reporting window, it would skew the ROI.

I'm not sure if this is the same thing as what you cited, as my argument is about the cost association during the reporting window as opposed to the future revenue association. I can't figure out a way to back those out in real-time (i.e. in enough time to make adjustments to the campaign) though.