I worked with the mobile team at a social gaming company to develop a complete set of use cases for a complex mobile product and its interface points with an existing web game.
Sometimes, the best way to design a good user experience is to enumerate all the possible types of users. Who are they? What are they like? Do they have iPhones? Do they have Facebook accounts? This was precisely what I did with the mobile team at a social gaming company – I fleshed out their user base to steer their product development towards putting their users first.