Yes, mistakes HAVE been made, and by those very people who told us (although not all of us believed them) they knew what they were doing.
Those "mistakes" have cost over 2,000 Americans their lives, yet neo-cons think nothing of laughing at a picture in a ladies magazine while failing to admit the inadequacies of their fearless leader.
You're right in that the borders of Iraq are "porous," but if YOU knew that beforehand, and I knew that beforehand, WHY do you think this, apparently transparent fact, eluded the military planners of this war?