ThetaBoard looks great, well done!

The model that seems to be working for social collaboration software and what Trello has announced, is the majority of user features are free while admin/control features fall into the paid version. Yammer's business model is not too different with admin/control features at the core of the paid version.

Organizations are willing to pay for control while users are less willing to pay for features.

If you can get widespread adoption by free users there's increased pressure on Management to signup for the control features. Someone else coined this as "Enterprise sales by the backdoor".

We're looking at a simliar model with http://www.taskmessenger.com

* edit for spelling