What do you want to see in a social task management app/service?

I'm working on a social task management system, and I'm wondering what you guys would want to see in such a system.<p>Basically, it would let you create tasks and share/assign them to people (but it goes much farther than that).<p>Do you see yourself using it? As an advertiser, would you pay to make your advertisements into actionable tasks that people could add to their to-do list (or share with friends)? Would you assign tasks to your friends using it instead of asking them in person/by phone/by email?<p>I'm trying to identify as many use case as possible, so don't hesitate to share them here.