I'm a big fan of statistics, so I'm glad to see all the great stats on the site. Another interesting stat to include would be the value a project brings to developers. If projects can indicate which other projects -- particularly frameworks -- they rely on, it would provide a display of how much it costs to develop using a particular framework.
This would be particularly useful to project managers looking to choose a framework for a new project, as they could easily see the average cost of development using a variety of frameworks and make a more informed decision.
Existing data should be sufficient to support this. Tags certainly won't cut it on their own, but the "What open source projects did you use?" section of the contribution form would likely do the trick. It would depend on how people are using it, of course, but I expect it would work, anyway.
It would then also include people who used open-source editors to develop an unrelated project. That would certainly speak to time savings, and since COCOMO factors in both lines of code and time spent, I think it would work quite well.