For typical marathon training, breaking 9 miles, 14 miles and 22 miles was always the toughest for me.
I used to be all about the specialized nutrition when I was doing triathlon; I think alot of it was more of a solution in need of a problem. Any performance enhancement was probably placebo effect.
I would take salt tabs and noticed that I would just sweat more salt...to the point I would have salt stains on my clothes. I would take salt and still have muscle cramps. There is an active area of research that suggests that muscle cramps aren't even linked to dehydration; despite what Gatorade says.
I think the secret about energy drinks is that it is flavored more than it contains electrolytes; it entices you to drink when you don't feel like it (I've never really experienced "thirst" when racing).
As for nutrition/carbs, just about anything will work as long as you can keep it down, its something you want to eat, and your digestive tract is still functioning (it shuts down at high intensity levels, as your blood supply is diverted away from it and to the muscles).
Seems like triathletes/runners/cyclists are all about the specialized nutrition. If you know any ultrarunners, they are scarfing pizza, peanut butter&jelly and cookies during their races. Kind of interesting.