I was talking with Marcus and Nate yesterday about the stomach troubles I have when running longer distances (in excess of 13-14 miles). And, now that I'm planning on running another marathon... I think it's only right that I start trying to figure out the right combination that will make my stomach less of an issue.
So... I was playing around on the Runner's World forums and ran into a post about this exact thing. It linked to a pretty good document called, "The Endurance Athlete's Guide to Success: Everything you need to know about optimum caloric, electrolyte and fluid intake for training and competition".
I'm gonna read this and see if anything jumps out at me. Hopefully it will point me in the right direction. Hope you enjoy it too.