Great article that provides invaluable insights into Mailchimp's experience with the freemium business model. We are using a freemium model with Domainer Income (<a href="http://www.domainerincome.com" rel="nofollow">http://www.domainerincome.com</a>). Now, we are still in the throes of improving many aspects of the site and conversion funnel, etc but with regard to the freemium model itself, it occurs to me that we have - and anyone deploying a freemium model has - quite a few variables to play around with that will impact the 10:1 ratio as well as overall conversions, sales, profits, renewals, etc. For example, my experience and observations suggest that you really need to provide overwhelming value in the paid version to get people to upgrade. 'A little bit better' won't cut it. Also, you can experiment with the actual free/paid service you provide. One thing we're about to do is give everyone who signs up for a free membership a trial of the premium service before they are 'dropped' back to the free account. These are just two examples. On the other hand, having said this, I am also developing a theory that you really have three target markets: freebie users who will never upgrade, paid users who want the value-added services of the paid version, and a group in between that will upgrade if they perceive enough value in doing so. How big is the middle group, what will it take to convince them to upgrade, is it cost-effective to try to persuade them? These are all fascinating questions!