Lt. Gen. David H. Petraeus on the effort in Iraq:

It's like trying to build the world's largest airplane, while in flight, and while it's being shot at. 

There's more interesting stuff in Petraeus' interview with The Tampa Tribune. By the way, The Trib is running a series of interviews with military personnel who've recently been on the front lines of Iraq. You can find the rest of the interviews here.