At a little after noon EST, Jane Arraf on CNN is reporting about 30 percent turnout in Baqubah, a mixed Sunni-Shiite city to the northeast of Baghdad. It seems clear that the turnout was largely Shiite.
Although the violence and attacks have been extensive and took place all over the country, the security measures put in prevented massive loss of life. Suicide bombers clearly could not get close enough to crowds to take a big toll.
On the other hand, if the turnout is as light in the Sunni Arab areas as it now appears, the parliament/ constitutional assembly is going to be extremely lopsided. It would be sort of like having an election in California where the white Protestants all stayed home and the legislature was mostly Latinos, African-Americans and Asians.