Good article in the Daily Kos about the growing split between Dean supporters and the so-called mainstream Democratic party: The battle for the soul of the Democratic Party.:

...the hatred the establishment feels against Dean has nothing to do with ideology. Dean hasn't paid his dues with the establishment. Dean campaign manager Joe Trippi has made his name working the campaigns of insurgent (hence anti-establishment) candidates like Jerry Brown. He is not part of the chummy inside-DC club of Democratic Party consultants.

If Dean wins the nominantion, he becomes the head of the Democratic Party. He gets to replace McAuliffe and fill the top ranks at the DNC. Suddenly, a "DNC Chairman Joe Trippi" is a real possibility, and for an establishment that has spent the better half of the last decade laughing at Trippi's antics and dismissing him as a kook are suddenly standing on shaky ground.