Captain's Quarters breaks it down:
This couldn't have come at a better time. Congress has tied itself in knots trying to opine on what a disaster the surge will be, and before they can vote on a resolution scolding George Bush for wasting resources, he's already chased one of the worst actors out of Baghdad. Nancy Pelosi will be holding a debate to disapprove of a strategy that has already demonstrated success...
This demonstrates that the US forces have seized the initiative in Baghdad, and that the Maliki government has apparently completely abandoned Sadr. It's a tremendous victory in the preliminary stages, and it sets the table for an end to the hottest part of the insurgencies in the Iraqi capital.
Update, 2/14/07: Yet, the Democrats are going to "stay the course" with their undermining.