The partitioning of Iraq would be a terrible idea - and that's what makes it so great if the US is looking for an effective strategy to force the international community to become more active in managing Iraq, and to lessen their own burden of occupation. That the Bush administration has publicly ruled it out has nothing to do with whether or not it's still seriously on the table. In the worst case scenario, partitioning Iraq would force Iran to lay their cards on the table - a partitioned Iraq would be the best and only serious chance to grab Shiite-held territory. The same would go for Turkey and the Kurdish factions. To top it all off, it would be the EU and the UN who would be compelled to step in and try to manage the various sections - it could be like the World War II Occupation Class of 1945 reunion with the US, Britain, France and Russia. Nothing whets the international diplomatic community's appetite like the possibility of drawing borders, mandating behavior and ceasefires violating a nation's sovereignty to bring about peace. Let other people go in and draw the ire of Jihadis and the other friendly neighborhood militants. We will hold and secure American section - and we'll pick the best and friendliest one of course - and then we'll see who can best keep the peace. Relieve US forces of the burden of trying to manage the whole country. Let's take one section, put everything we have in it, and let the other parts of Iraq compare life under the Islamists and other incompetent fanatics. Heck we could even make it some form of "Big Brother". Every 6 months, the occupying nations take votes to see who has to pack up and leave Iraq.
This would also be an interesting way to stimulate the creation of an active, Iraqi identity. After all, nothing makes you think more about who you are, as a people, until someone tries to take that identity away from you.
If nothing else, keep in mind that there is now a new UN Secretary General - Ban Ki-moon - and there will soon be a new US president. Even Putin will eventually step down from power, in theory. Who's to say they won't reconsider partitioning? And who's to say it really won't work out?
Well, besides common sense. But whose common sense?