The Tiramisu project investigates how social media can provide new ways for citizens to take ownership of and responsibility for their public services. Initially we planned to make a system that allowed transit users to report problems and breakdowns in the service. However, after conducting fieldwork, spending time riding and talking with transit users, we came to realize that the uncertainty of using the service was the largest concern. In response, we made Tiramisu, a mobile app where transit users generate their own real-time arrival information by sharing location traces as they ride buses and trains. We released the app in Pittsburgh and users have share more than 100,000 location traces. We are currently working on a new version that supports rider to rider and rider to transit service dialog.