The recent bombing of a Shiite shrine by insurgents will likely have one of two possible effects. Shiites could respond by attacking Sunni holy sites (there are some unconfirmed reports of this already), or it could put one of the final nails in the coffin of the insurgency.
Although civil war is always a possibility, with Grand Ayatollah Ali al-Sistani calling for peace and morning, there is hope that it will be avoided. Also, there has been growing dissatisfaction with the insurgency even among nationalistic Sunnis - upset that attacks by foreigners are directed towards Iraqi Shiites and not Americans. I truly believe that Al Qaeda in Mesopotamia continues to alienate itself with attacks like this and will soon find that it has no domestic support in Iraq.