The live steering infrastructure allows you to interact with the simulation while it's running. That's good e.g. for changing model parameters on the fly. In situ visualization allows you to view simulation output while the job is still running. Particularly interesting is Björn Meier's output plugin which connects LibGeoDecomp to VisIt via libSim. VisIt is a scalable, feature-rich and generic visualization tool which is suitable for most scientific simulations. Libsim allows VisIt to pull data directly from a simulation code at runtime, without dumping it to disk. It also enables VisIt to controll the simulation's time loop. These features are slated for a later release (0.4.0), hopefully ready at the end of this month. Looking forward to see you in San Jose!
Update The time and location of the talk have now been finalized: Thursday 03/21, time: 16:00-16:25, room 211A, McEnery Convention Center.