Use KeyPad Navigation to get to an appointment you want directions to. Press 0, when prompted, right after listening to the text of the appointment.
At the beginning of a call press 0, for applications, and then 0 again, for driving directions. You will be read a set of locations, drawn from your upcoming appointments. Press the number of the locations you want to go to.
Throughout the RoboCal interface, pressing 6 means go forward and pressing 4 means go back. Pressing 5 while listening to appointments means you want to drill down, and hear more details. While listening to to driving directions 4 and 6 again mean forward and back, but 5 means pause.