If you want to be really cynical, you could suggest that the early hand-over of power was really a ploy to boost Bush's slumping ratings in the polls...

As for troops, theoretically, the new Iraqi government has the right to kick us out now, though that would probably be counterproductive at this point, and the U.S. government wouldn't install an Iraqi government that was unfriendly to having permanent U.S. bases there. Still, having bases there is a lot different than having a full-scale army there, and would eventually allow reserves to return home. I am aware, however, that even with the handover of power, our government has said that we won't pull troops out until the Iraqi government can defend itself.