Well, if you consider the fact that we need to win the war NOW and worry about out-year retention later, the surge makes perfect sense.
What we really need is (a) a surge that is big enough to pacify Baghdad considerably for a long enough period of time to 'take hold', and then have mixed US/Iraqi forces that gradually hand off the *pacified* area to Iraqi forces who are then *capable enough* to keep the peace.
The missing link has in the past always been the fact that the Iraqi forces have cracked under the pressure of excessive violence and/or were compromised in some way.
Well, if you consider the fact that we need to win the war NOW
It take around 10-12 years to win a guerilla war. So I wouldn't expect this to be over anytime in the next two years.
But if Petraeus thinks this will work, and given he's forgotten more than I know about this kind of stuff..I defer to him.