How BusinessWeek measures user engagement

How do you get past those squishy pageview and unique visitor metrics and instead measure how users actually respond to the content you produce? My interview on this topic with BusinessWeek Online editor John Byrne (whom I met in Perugia at the International Journalism Festival a couple weeks ago) is now up on OJR. An excerpt:

Byrne: User engagement is how we nurture and build a community. Our reader engagement index is a comments-to-postings measure for a given month: So we will tally how many comments on X number of stories/blog posts that published that month. This gives us a ratio figure that we track to determine our monthly reader engagement index and growth.