According to Andrea Mitchell who spoke today with intelligence officials and has just revealed this in discussion, Iran is the official target and that's why Condi is flying east today -- to alert the Saudis and others.
Update: Apparently Stratfor confirms that "this latest gambit is also directed at Iran."
According to Stratfor the goal of this is to force Iran to meet the Bush goals for a negotiation. They point out that the new troops will not be in Iraq immediately and it will give Iran time to offer a deal. Whether is accurate or will work is not at all clear.