There's a website Alexa.com that provides usage stats for the top 100,000 busiest sites on the web. I guess it's mostly interesting for advertising purposes. I was tipped off by Keith at SMC when he mentioned their Alexa ranking in a thread.
I've visited several times (sorry, be we haven't cracked the top 100,000 yet) and I noticed that all the woodworking forums that I could find in the top 100K show usage trends that are all following a similar pattern.
I isolated the forum URL's from the hosting sites, eg
"forums.taunton.com/fw-knots/" rather than "Taunton.com", to focus only on woodworking forums.
So without further ado, here's a link to the chart I created. The graph is interactive so you can plug in other sites or change the time span.
Lemme know what you think about the trend and what might be behind it.
Have fun !