Community leaders share a number of metrics to communicate ROI back to their management and stakeholders:

• Page Views: This is not an insightful metrics for most communities, but it is essential to understand page views for ad-driven communities in order to establish CPM rates
• Registrations: Membership of a community, which some tie to “awareness”
• Satisfaction: Satisfaction with the community as well as with the host organization
• Downloads / Trials / Lead Generation: Software companies and communities with a
  premium (paid) layer can compare this metric with other marketing activities and
  channels
• Cost Savings: Cost displacement or reduction as a by-product of community activity  This could be call deflection for support communities, or R&D benefits for product teams
• Content that ties back to “Mission”: This is particularly relevant for non-profits, who generally have a very clearly defined mission. Showing examples of content and
  activity that support an organization’s mission help justify the return on the community investment by demonstrating effect
• Direct Revenue: Perhaps the ultimate metric is showing direct revenue from a community;  and comparing revenue (and donations) from members and non-members is becoming possible because of better metrics

Source: Forum One Communications