Blogospheric pressure

There's a much discussed question as to how much the blogosphere has helped the right and the left. The most recent post I've seen on this was here at Craig Westover's site. Usually the argument from the right is that the blogosphere has increased the variety of discussion on the right while it's hurt the left by empowering their more extreme elements. That's made it easier for Republicans to be the Big Tent party while making it harder for Democrats to grab any part of the center. Craig notes that

Aside from some challenging ideas from liberals writing about legal theory and jurisprudence, there isn't a lot of challenging liberal writing, and what there is tends to be more libertarian than "big government" liberal.

This tracks with my own experience as well, though it should be noted that the argument quickly becomes self-serving in a 'our side good, your side bad' type of way. But the question is worthwhile. Maybe more importantly, why is this so?
It's important to remember some short-term issues that have shaped the blogosphere so far. The most important is that the left has been out of power as blogs have blossomed. They've felt more need to attack while the right has been been the governing power. Only when the Dem's win through can we test if those roles are ideological or situational.
The other important issue has to do with the way the 2000 election played out. With the protracted fight in Florida it set up a dynamic in which the losing side was bound to find the winner illegitimate. This only increased the passion on the left. If the 2000 election had been won by a 2004 margin the blogosphere would probably be a different place.
There are some longterm aspects which I think are important too. One huge benefit to the right is the way that blogs have empowered libertarians. Libertarians tend to reject the methods of concensus that makes party-building possible. They haven't been able to organize into a bloc that the Republican party respects. The blogosphere has changed that. Not by building a bloc, but by giving libertarians a louder voice. Blogs like Instapundit and the Volokh Conspiracy have had a large role in making the blogosphere what it is. They've helped broaden the tent. Libertarian blogs have also played a role as watchdog when it comes to congressional spending, probably the biggest weakpoint in Republican performance. This has helped Republicans because it helps them return to their principles of small government.
What's happened on the left? They've become organized. They've developed communities. They've become burdened by groupthink. They've developed the 'netroots' phenomenom which empowers activists. In other words, they've given the activists a louder voice. I suspect that this has made all of the difference.