I thought Alexa had a kind of graph to show how a website's activity was progressing over a period of time. I wanted to see how Knol had evolved this year, but I am having trouble finding this on a graph.
I can't even find an Alexa page dedicated to knol.google.com to see it track such activity.
How much a site is stagnant/active is subjective, but even though it is not perfect, at least some metrics could be used: incoming links, traffic, content updates, and how often the website's name appears in discussions.
Is there something else perhaps that tracks this?