Using Alexa.com, we can compare activity on four important websites: barackobama.com, the site of Organizing for America; Tea Party Patriots, the Tea Party website; gop.com, the official site of the Republican National Committee (RNC); and democrats.org the official site of the Democratic National Committee (DNC).
The chart shows that barackobama.com has clearly been busier than the other sites over the last three months.
The Tea Party site held second place for most of this time but both that site and the RNC site have disappeared off the scale in late August.
Another measure of netroots activity can be found on Facebook. Here are the number of fans for the official pages of the DNC, RNC, Democratic Senatorial Campaign Committee (DSCC), Democratic Congressional Campaign Committee (DCCC), National Republican Senatorial Committee (NRSC), and National Republican Congressional Committee (NRCC).
DNC -- 114,731 fans
RNC -- 176,728 fans
DSCC -- 138,723 fans
NRSC -- 19,722 fans
DCCC -- 169,875 fans
NRCC -- 11,241 fans
So, with exception of the DNC Facebook page, the Democratic pages are more popular than their Republican counterparts. Unfortunately, I haven't been able to find a way to track activity on those pages. However, the DSCC and the DCCC pages are noticeably much more popular than the corresponding Republican pages on Facebook.
Just a brief spot check, but from the looks of it the Democrats look like they are beginning to push things online, which is a good sign.