Bush has said from the beginning that once the Iraqi government doesn't need us, he'll pull out. However, the Iraqi government is a farce and a bunch of yahoos who are more worried about offending each other than unifying Iraq.
The mission in Iraq for the US military is shifting from combat to training, and then we will slowly be phased out of Iraq...but that doesn't mean that we're coming home. We'll just move back into Kuwait just like the last 15 years for Operation Southern Watch. The US never completely pulls out of a region when they've gotten a foothold on it unless the foreign government ORDERS them to.