My philosophy on long-run intake is to try to mimic the race as much as possible. So look forward to your target marathon and find out what type of sports drink they will have (Gatorade at Chicago in this case) and bring BOTH water and Gatorade on your runs. Diluted Gatorade or any other "personalized" fluids will be great for when you are training, but those won't be available during the race (unless you bring it along with you, which would be annoying), so it's kind of pointless. As much as some people rip on them, I recommend wearing a Fuel Belt (the four bottle kind), where I will fill two bottles with only water and two bottles with normal Gatorade (non-diluted). The small bottles let you mimic a race, as you can just take two quick swallows of each at pre-determined points during your long run (I usually do every 2 miles during the summer), and you don't have to lug around a big bottle of water in one of your hands, since the belt sits around your waist. It will take a time or two to get used to having the thing around your waist, but eventually you just forget about it. Just my recommendation on what works for me.