If I'm trying to reach a big goal, like "run a marathon" or "bench-press my weight" or "launch my site", the way to do it is to break it up into bite-size chunks with discrete milestones.

It'd be cool to offer some "goal templates" (e.g. "how to train for a marathon"), and allow folks to make and share their own templates. Match up folks with similar long-term goals to form a support network. You could even use that to jump-start the community... market it to a group of people (e.g. marathoners) who are already working towards some big goal.

Plus, this could be the basis of a better encouragement system. If every day's goal is the same ("run"), I don't have any particular reason to cheer you on the 12th day any more than the 9th day. But if you reached a specific milestone on the 12th day I'd give you props.