Lika your start. It seems from your suggested KPIs that they cover many different situations och online environments.
- The membership measuerement is valid for formal memberships lika MySpace, groups in Facebook, Ning etc.
- Newsletter and subscribers are more focused on web sites, than for instance Facebook groups?
- Active versurs passive behaviors are very different depending on situation, do you think the same KPI could be used on forums, online social networks, websites, blogs, and also mirco blogs?
At least 1 measure should use median instead of average:
* the number of friends per member
because there is a power distribution. If You are using average, the activity is strongly underestimated.
I am also not sure if average time to last visit can be considered as a measure of activity. Do anybody know what is the typical distribution of such variable?