The practice/qualification utilisation charts use the Protovis donut chart style (a variant of a pie chart) to produce a macroscopic view over the way each driver and each time made use of the corresponding session.
Each pair of rings represents one team. The outer ring is the lower numbered driver. The teams are order from left to right, going down the page (so top left is Red Bull, top right is McLaren).
360 degrees corresponds to the largest elapsed session time measured from F1 timing sheets from across the drivers. An incomplete ring shows the driver did not use as much of the session as did the driver who made most use of it (which is my estimate for the available session time).
Each segment represents a different time recorded lap on the FIA timing sheet. The angular distance, and hence length of the segment, represents time.