Signs of Life
From Social Patterns
The easiest way to communicate to your returning visitors that your social environment is lively is to present them on login with a summary of recent activities, ideally those of people you’re connected to, although for new users it may still be worthwhile to show them examples of recent activities (perhaps anonymizing the identities of the users to preserve their privacy from strangers). This is what LinkedIn does, and it doubles as a reminder to the user of the range of activities they can engage in within the service.
Similarly, when you log back into a project on Basecamp, it shows you not only who is participating in the project, but whether any of them are currently online, or how long it’s been since they visited.