My personal experience: I ran a 3:39 marathon at Flying Pig last year. I had a first marathon (OBX) under my belt, and raced a half marathon 3 weeks later for a PR. Then, for the next 4 months, I built up mileage by 2 miles per week, peaking at 60, then dropping back as necessary for the Louisville Triple Crown (5k, 10k, and 10 miler). I also ran the Louisville half marathon (Kentucky Derby Festival mini/Marathon) for a PR the week before Flying Pig.
I was in a car for about 2 hours the day before the Flying Pig, and ate poorly (mexican and pub grub) the night before. Of course, I know someone who PRed by 15 minutes and BQed on Cracker Barrel. The main nutrition change was pacing of calorie intake during the race. I took a gel every 5 miles, versus 6 miles for training. I also made a point to get some Gatorade at every oppotunity, versus water alone during training.
Of course, the one downside is that gels and gatorade are nasty together, especially when you mouth is somewhat dry from running. I didn't take them simultaneously (grabbed water at the stops as well), but the effect is pretty close. I'm also guessing that there were way too many salts in the gels and Gatorade, although I never go for Gatorade with extra sodium content.