This is an idea first proposed by Vice President Biden in 2006 when he was a senator. It was a non-starter then and it won't work any better today. While the Kurdish region in the north is already almost an independent country, neither Shiites nor Sunnis are interested in splitting up the rest of Iraq—something that would be hard to do, in any case, because the two sects are intermingled in Baghdad and other areas. Just as the solution to Iraq's last major bout of bloodletting, in 2003-2007, wasn't partition, so it isn't today.
What is? The same thing that worked during the 2007-2008 U.S.-led "surge" to bring down violence by 90 percent: the implementation of a comprehensive counterinsurgency strategy that included political as well as military components. What really made the surge succeed was the outreach by U.S. commanders to the Sunni tribes of Anbar Province. Prime Minister Nouri al-Maliki, after spending the last few years victimizing Sunnis, needs to undertake similar outreach to convince the Sunnis that they will be able to prosper in the new Iraq. Otherwise, many Sunnis will tacitly or actively support Al-Qaeda in Iraq, which is trying to position itself once again as the champion of this embattled minority.
Al-Qaeda's success is evident in the fact that its fighters are openly parading through Fallujah and Ramadi. Those cities are becoming de facto part of a new al-Qaeda statelet that spans western Iraq and eastern Syria. Separating this region from the rest of Iraq will make permanent this parlous state of affairs. What this region needs is pacification not partition.