I'm back to thinking I won't do another marathon until Spring 2011.
In the meantime, I should talk to some other runners about what I could do differently or better. My goal race pace on Sunday was 5.2 minutes (5:12) per km. For the first 10K I planned to go at about 5.5--I actually achieved 5.4, for 54 minutes to that point. I deliberately picked up the pace, and for a while my watch along with km indicators suggested that I was doing 5 minute pace--which would get me up to 5.2 overall at the half mark. Instead, at the half I was at 1:53, three minutes behind. From then I was trying to catch up, and then I hit the wall at 6K before the finish.
Maybe it's better just to try to stick to your goal race pace from the beginning?