There was an article in RW this issue that helped unveil some mysteries surrounding my pukey and poopy episode a few weeks ago. As many of you reported, it's not uncommon for you as well, and according to the article, it's a very common running problem. Running, I guess, can be a little tough on the guts.
First of all, all exercise is irritating to the stomach because blood is drawn away from the stomach to the muscles, but runners report more stomach upset than, say, swimmers or cyclists, and RW says this is because running has so much impact, so much jostling, that the stomach and the whole GI tract get upset. This can prompt diahrea, vommiting, and gas (all lovely side effects).
This explains why so many runners have reported similiar stops at gas stations. Runner's World suggests tweaking your diet until you find the right combination that eases your stomach, and to make sure that meals are spaced appropriately before running. And the article suggested a few foods to avoid or replace (obviously having a bowl full of high fiber cereal and a cup of coffee before a run will lead to trouble). The article helped me feel a little more normal, and gave me some helpful suggestions.