While the Zarqawi-ites may revel in the short term chaos that they've caused this move is a colossal, strategic blunder on the level of 9/11. The intent of this attack and the scum behind it is too obvious. The Shia aren't behind (though I'm sure Michael Moore can find an agent provocateur conspiracy), the Sunnis would be insane to try and it sure ain't the Coalition. That leaves the insurgency which begs the question why? Well when does a team do a Hail Mary - when you're running out of time and there's nothing left in the playbook.
The interim Iraqi government, the new Iraqi Army and the Coalition must ensure that the violence is controlled, diminished and finally extinguished. If it means martial law and curfews, that's acceptable in the short term to ensure that this becomes the epitaph of the insurgency. Overall the political and religious figures in Iraq are calling for calm and not point figures at anyone other than the insurgency.
James Robbins at NRO has the same idea.
Despite panicky headlines to the contrary, it is not in any group’s interest to wage full scale civil war in Iraq. The Shiites have power without it; the Sunnis could not win it; and the Kurds will sit it out either way and keep patiently building their homeland. So this senseless act of violence against the final resting place of two of the most respected figures of the Muslim religion only proves to the Islamic world that al Qaeda and its allies are true heretics who care nothing for the faith and are out for power by any means at their disposal.
Iraq the Model has a great on-site report.