The JournoList story is an inside baseball tale, but what's fascinating about it is that it proves what conservatives have argued for 30 years: there really is a vast leftwing conspiracy.
I think JournoList is—or was—fundamentally different, and not simply because one of its members proposed to make palpably false accusations. As best I can tell, those involved in JournoList considered themselves part of a team. And their goal was to make sure the team won. In 2008, this was Mr. Obama's team. More recently, the goal seems to have been to defeat the conservative team.
Ezra Klein and others have argued that it was mainly opinion people and columnists saying the outrageous things about Rush Limbaugh, Fred Barnes and Karl Rove. But while people who aren't beat reporters might have been commenting on JournoList, there were 400 subscribers and more than a few of them were mostly reporters and editors, the regular kind who talk about professional ethics and objectivity. How many of them read the JournoList posts without making their own comments but who absorbed the ideas written there? Until the list of subscribers is revealed, we won't know.
UPDATE: More at Townhall.com, where the 3 theories of media bias are discussed well.