Among the many different kinds of screens found in community-driven Web applications, two screens in particular define how content creators stay engaged and contributing: social objects and dashboards.
Social objects are the artifacts that bring people together around shared interests or topics. They are the content assets around which communities form and grow. For a community-driven site like YouTube, the social object is the video. For a community-driven site like Flickr, it is the photo. For a social network like Facebook, there are many social objects but the most engaging are probably photos and games.
Because the social object is what brings people to a community-driven application, its screen design matters a lot. The object needs to presented appropriately and framed with lightweight actions that allow people to share, curate, and discuss. These actions allow consumers of the application's content to quickly and easily provide feedback to the application's content creators. This feedback encourages creators to share more content assets and the cycle continues.
Working through the design of the social object page forces you to first define what that object is for your application and second understand how your users need to interact with that object.
While the social object page creates opportunities for engagement, the dashboard page summarizes the results of that activity for content creators. Ideally this activity gives content creators a reason to return and ultimately contribute more. Working through the design of the dashboard screen requires an understanding of what activity matters most to content creators and why.
Because of their role in keeping both content creators and consumers engaged, these screens are probably the first two you should design when thinking through the dynamics that make a social Web application tick.