Metrics for Discourse "pilot"

As an exercise and to help us move forward with Discourse, we’ve filled out the Pilot proposal doc retroactively. One of the things this has helped us think about is the metrics we need to show that Discourse has been successful, which ones are currently available in Discourse and which need to be added.

Pilot doc - https://docs.google.com/document/d/1hVVQYggCaiS6K2nJmT-C_oQQwlG72xLdCvGSwoTbi94/pub
Pad for brainstorming on metrics - https://communityit.etherpad.mozilla.org/Discourse-pilot-measurable-impact

@leo - what is the progress for figuring out how many people have posted in a particular category?