I think these are some very interesting visualizations, though obviously they are only mining commit data, not patch data, which doesn't account for all the contributors in many instances.
See examples:
http://github.com/mpdehaan/cobbler/graphs/impact http://github.com/mpdehaan/func/graphs/impact
You can see Func had some initial collaboration that was interesting and then a spurt during Google Summer of Code. Cobbler's really only gotten a good spurt over the last year, but is shifting to at least 50% outside contribution. (A /ton/ of outside patches happened via me applying them though)
While this data is skewed from only tracking things with git attribution, increasingly though, more contributors everywhere are using github, leading to better data.
The reason I brought this up is that this widget could be a very interesting way to prevent list activity over time -- and maybe we can borrow from the idea.
--Michael