User group downturn?

[Dave Smith]

I've been thinking a lot lately about the downturn in user group meeting attendance and mailing list participation over the last few years. Today I graphed Plug's mailing list activity from 2005 to present (messages per month), and noticed a startling coincidence.

Is this causal or merely correlated? Did other groups see a similar downturn in mailing list usage?

    http://thesmithfam.org/images/plug-stats.png

FYI: The arrow in this graphic is pointing at September 2008, the month StackOverflow started its public beta.

--Dave