A ways back I linked to these two reports
by Michael Totten on Iraqi Kurdistan, illustrating how enormously different (and more successful) it is from the rest of Iraq. Here's Totten's report
on his visit to Kirkuk, a city at the border between Iraqi Kurdistan and the rest of the country, whose former Kurdish population was reduced by ethnic cleansing during the rule of Saddam Hussein. Because Kirkuk dominates the oilfields of northern Iraq, the future status of the city is fiercely disputed; even Turkey is trying to interfere, due to its concern that an Iraqi Kurdistan including Kirkuk would become so wealthy that it might be a little too appealing to Turkey's own large Kurdish minority.
Whatever the merits of historical precedent (and we all know how tangled that
kind of question gets, especially in the Middle East), it seems obvious that Kirkuk itself would be far better off being incorporated into Iraqi Kurdistan.