Yes. The US should withdraw it's troops from Iraq. The insurgency in Iraq is born of people with extremely strong religious beliefs. This belief structure dictates that they will do anything at all to defeat an enemy. A paid soldier in the US military can fight with the best technology on the battle field, but if the enemy is willing to die immediately for his cause, then it makes it very hard to win that war.
While the American presence within Iraq has succumbed to negative feedback, I do not believe that their efforts are in vain. Insurgency within Iraq, while prominent, is not unlike insurgency within other countries. Major factions of "terrorists" exist within countries worldwide, it is simply political spin that has soured the efforts of US Troops. Whether measurable or not; they are still helping.