This is a bit late but finally getting to this!
To recap, the build to this NYC Marathon was only about 2 months. Very short, but I got there without too many problems in my muscles.
NYC was very chilly, although there was a warming trend. The morning of the marathon was still very chilly – 42 degrees or so! I got out there early as usual. Nearing the start of the race, I of course butted my way up as far to the front of the line as I could get. But with 45,000+ people racing, I realized that the field was going to be full no matter where I would be – there was just too many people.
Everything was going great until I hit mile 18.5. Here is a screen shot of my pacing from my Garmin 305 watch.

I was at a very fast pace, just racing by perceived effort to the edge of my threshold pace. But as my pacing showed, and what I remembered from the feeling in my legs which were getting tighter and tighter, I was slowing down bit by bit.
I did manage to hit mile 13 at 1:43, or about 1:42 at my chip time. This was on pace for a sub-3:30 finish, assuming I could hold that. But of course I could not.
At about mile 18.5, I cramped which ruined my day. You can see the HR drop on these graphs, along with my pace.

After that, it was a constant cycle of walk about 2-3 minutes until the cramp spasm goes away, and then run until the cramp started again.
I still managed a 4:02 chip time but it wrecked my 3:30 goal time.
Observations and learnings:
1. It is possible for me to build to marathon fitness in only 2 months. It verifies my previous coach’s teachings, which is that you can build to endurance racing fitness by ramping volume only in the last few months of training, rather than maintaining a volume program for longer periods of time.
I would not recommend this to beginning marathoners. I think there are many variables that make it possible for me to have built successfully to marathon fitness in so short of time, not the least of which that I have now many years of endurance racing under my belt.
I signed up for the LA Marathon 2012 in March next year. I hope to build, starting Jan 1 so I’ll have about 2.75 months to build to that race. This is still not the typical 4 months or more that I usually like to have to build to a marathon, but having done so with NYC I feel confident that I can do it again.
2. The cramping problem is one that I have faced for many years. At the NYC Marathon, the day was relatively cool so temperature was probably not the factor in making me sweat too much and lose too many electrolytes. I also was taking electrolyte pills, about 1-2 per hour. My best guess is that I did not have enough strength to maintain my level of effort over the full 26.2 miles.
To remedy this, I am back on my Russian strength building program and hope to be deadlifting over 200 lbs by the time Jan 1 rolls around. I need to be stronger at a 3:30 pace or else I will risk cramping again.
I am back on my ASR Speed program and will be working on my speed, as well as strength building, until the new year. Then I hope to use a fast build to the LA Marathon, like the one I used for the NYC Marathon.