Abigail Benson - we focused on core / founder members in the initial days and they helped build the momentum. However, as Joel (Salesforce) said - it's all about the value your members get from the community.
The value can be a result of the content or network that community offers.
It looks clean. The only limiting factor I see is that it keeps everything in the 'discussions' format. Modern communities need more than simple discussions.
I have known them as a platform for social media management; but not as a community platform. Caitlin - what's your evolution criteria for the platform?