Sauber have an interesting slot which ducts air from the underside of the nose, and discharges it behind the step on the top surface. Craig Scarborough has a diagram of the slot, and Giorgio Piola also has an elegant drawing of the feature in this week's Autosport.
The best explanation of the slot is that it removes a portion of the boundary layer from the underside of the nose, using the low pressure created on the top surface when the air accelerates over the step. The thinner a boundary layer is, the less liable it is to detach, hence a thinner boundary layer beneath the nose could potentially enhance the quality of the airflow fed to the underbody of the car.
What Sauber have done, then, is to carve the aerodynamic equivalent of a flowing artesian well, using the pressure gradient between the lower and upper surface of the nose. It is yet another ingenious example of the karstification of Formula 1's aerodynamic landscape.