As I've said several times here, there is no gold standard for measuring success in a community. In my opinion, the trick is to embrace the ambiguity and remember to tie metrics directly to your business goals. As creatures of parsimony, we're compelled to want a simple formula for "healthy" communities. Most likely your answer will not be in page views. Likewise, it's not embedded in the illusory grail of "engagement."
I'll go into more detail on the webinar; for now, a few things to keep in mind as you seek to quantify your efforts online:
1. All social media create rich social networks; don't ignore social constructs. Think connectedness, reciprocated communication, resonance...
2. Adding things together may seem fancy, but really it's Noisy and messy. You've heard it before: don't measure something simply because it's there to be measured.
3. The metrics that tap into the depth of members' immersion in a community are not ROI per se. First measure something social; then use it to predict your business goal (e.g. Retention, Satisfaction). Then, calculate your ROI ratio.
Remember, having a measurement strategy is not about having a belt of metrics, but a framework within which you can measure your success toward a specific business goal.