Nice accomplishment but I have to say that the idea of the product is off-putting. Still I guess it's up to people if they want to advertise this way.
I'm not convinced that this approach will always yield a higher viral coefficient than not forcing sharing in order to gain access. The interesting thing is you could actually run A/B tests on this.
I'm looking forward to running lots of different A/B tests. I can change the "Download for Free" button, change the copy on the Share popup, and change how people interact with the share buttons. I definitely want to make sure I optimize the site, not just for me, but for the people who are using it to distribute their content. The purpose is to get them a larger distribution network so I'll try any changes that accomplish that.
I'm not convinced that this approach will always yield a higher viral coefficient than not forcing sharing in order to gain access. The interesting thing is you could actually run A/B tests on this.