My concern is that even if you have access to the project timelines it's hard to compare projects (unless they are doing the same project over and over again). As well, it often takes some period of time (maybe months?) before you might have enought 'projects' to actually evaluate the impact based on project timelines. SO, I think there are other ways of evaluating the impact and we should work at brainstorming some of those.
What other, maybe indirect, effects could you examine?
One way I can judge the impact is with the satisfaction of
A. Mr. Fitzpatrick
B. Development volunteers
C. Site users at large.
Also (and this is closely related to C., above), another measurement could be site uptime. Currently the site has what I believe to be a scalability problem, and sometimes goes down (especially for users of the free "light" service). Perhaps some company projects have to do with better uptime.
Those are just initial thoughts. I can also ask Mr. Fitzpatrick his views on the subject.