From my understanding, soluble fiber is important for softening the stool but insoluble helps move it through faster so that it can't harden. We recently came to the conclusion that I was getting too much soluble, as compare to insoluble, because I would get hard stools even with huge fiber and water intake. It turns out that I was supplementing my fiber intake with mostly "fiber added" food (like "Fiber One" pop-tarts, yogurt, etc.), which, it turns out, has mostly soluble fiber. So we are trying to tilt the balance in favor of insoluble by being aware of the actual breakdown in foods.
Finding the actual fiber breakdown is difficult. The nutrition facts on food packaging will tell you how much fiber is in it, but not what kind of fiber that it is. So we did some searching and my wife came across a nice website with breakdowns on soluble/insoluble fiber for many common foods:
http://www.feinberg.northwestern.edu/nutrition/factsheets/fiber.html
Hopefully, you guys find this useful as well. :D