I had a power point presentation which Matt Stoller helped me prepare. In it, I 1) explained what a blog was, with examples of comments, diaries, etc. 2) I said, "Blogs aren't ATMs, they are the beginning of a progressive noise machine. And 3) ignore blogs at your peril, see what happened to Daschle. There was nothing about confrontation or partisanship. I never spoke about strategy...
If I had to guess, I'd say the numbers are closer to 500K people who visit at least once a week. But that's at best an educated guess.
Those numbers are still probably more than the top opinion mags combined, however.
Anyway here's The Thought:
Blogs are "piecework" production of opinions, ideas and news; when accompanied by advertising, the writer is rewarded directly by the amount of click-throughs he gets generally, or the amount of eyeballs that visit the site (if its a big blog).
That's the real threat to the "mainstream media." Blogs screw up traditional media business models. Right wing blogs, like Hewitt's are an attempt to astroturf grassroots sentiment, but Hewitt's nonsense can't stop the upending of the traditional mainstream media business model, and its potential re-consolidation around content creators outside traditional venues.