In the goals section, under the "Contributes" heading, it will only show that one goal contributes to another if the contributing goal is in another section - for example, one long-term goal cannot contribute to another long-term goal. The contributing goal actually has to be in the short-term goals section.
Could this be an additional feature? Surely one long-term goal (say, "Get accepted to med school") could contribute to another long-term goal ("Graduate from med school.")
We wanted to extend our to-do functionality to match the six-level model described in David Allen's GTD book. He uses an airplane metaphor in the book:
50,000+ feet : Life
40,000 feet: 3-5 year vision
30,000 feet: 1-2 year goals
20,000 feet: Areas of responsibility
10,000 feet: Current Projects
runway: Current actions
20,000 feet and down was already implemented well with our folders/contexts/tasks and subtasks. This left 50k, 40k and 30k, which we mapped to Life, Long and Short term goals. We felt like this matched GTD well and was also accessible for people who don't use GTD.
We also try to keep things simple, and having a strict three-tiered approach keeps the interface easy to use and understandable to most people. If we allowed nested goals, or for goals on the same level to contribute to each other, then you could get into some complex situations that would be difficult to resolve or communicate to the customer.
While I agree that three tiers is enough, I am curious how you see 20k feet reflected in the toodledo schema. Runway is obviously tasks, sorted by context, and 10,000 is folders, but where do you think the areas of responsibility go?