Interesting idea. As I recall, Putnam does more than merely state that there has been a decline, he also posits possible causes and problems associated with a decline in civil society. (This is all from memory, it's been a while since I earned my Poli-Sci BS).
I like your basic angle and I do think that on-line communities such as Ubuntu, Wikipedia, etc. are now important parts of civil society for many people. But, there are some extra things I think you need to consider.
The more I think about it, I think you should try to do something around Ubuntu. It hasn't been done before (that I know of) and would thus be more interesting. But, it may involve a little hacking here and there to get at some interesting answers.
- The classical texts on civil-society were, by definition, constrained to national boundaries. Online communities are not affected by national boundaries, although they are affected by language, cultural norms, etc. Thus, if you want to really understand how much Wikipedia influences Americans (for example) you would need to constrain your numbers to IP addresses that appear to originate from the US (including Puerto Rico, DC, Alaska and Hawaii). Otherwise you are comparing apples to oranges.
- How do you compare the value of on-line communities to real-world communities?
- How does the Digital Divide affect this participation? For example, go into a public library (in America at least). You will see a line of people waiting for a few minutes on the computer. I am going to hazard a guess that most of the people who participate in the Ubuntu community do not do so from the public library. Thus, the digital divide plays an important role in defining who can and can not participate in these communities. (Other factors such as education, socio-economic status, etc. all play into the digital divide. The library riff is just an example.)
Either way, your first step is to develop your measurement. You need to define EXACTLY what your measures are for participation. Here's a quick (and imperfect) example (I don't want to be too helpful). You could develop a method to measure how many unique IP addresses contribute to Wikipedia articles in a single month. You could then draw a line graph that shows (I assume) that the number of unique IP addresses increases over time. You could then compare the number of contributors to the number of articles on Wikipedia during the same time frame.
Without looking at the Wikipedia database more carefully, this may or may not be possible. I dunno.
Similarly, you could count the number of "active" members on the Ubuntu Forums. Compare that to the number of downloads / "sales" of Ubuntu (of each release). You will (I hope) see that there are more members today than there were back in the Breezy Badger days. I assume there have been more downloads / Ship It CDs too.
But, I'm not sure how hard it would be to count active users. You could PM a couple of moderators for help. If you could talk to the people who run the Ubuntu Forums, I'm sure they could help give you the numbers . . . you just have to ask the right people!
So do a little digging and a little thinking. Wikipedia has a lot of information available about there articles and such. And I believe they make the IP addresses of people available as well. If you can find the information location / structure I'll help you write the SQL.
enjoy.