I think the end of 2012 is a good target date for us to be out.
The Iraqi army is performing well, but they are still quite weak in the area of logistical support. The Iraqi airforce is very tiny with no fighters or air defense capability. It's going to take several years before they can act without US air support. The Iraqi navy is small but performing well and is expected to more than double in size in the next 12 months or so.
They're off to a very good start but it'll be a while before we can completely draw down.