This isn't a public service announcement regarding your common garden 'Rake' but a feature on the nose down phenomenon used in F1 referred to as 'Rake' (The term however more than likely owes it's heritage to the garden rake as pictured above).
Creating downforce in F1 as we know is complex endeavor and requires one to think of the car as a whole rather than the sum of it's parts as by altering or achieving one effect can have a positive or detrimental effect elsewhere on the car. The word 'Rake' refers to the nose down pitch angle of the car and is most commonly referred to by the media as a sign of a team running with high rear end downforce.
These help to separate the airflow above the floor giving the exhaust plume a clearer pathway to the gap between the rear wheels whilst migrating the airflow coming around the Sidepods/floor into the more centralised coke bottle area via the tunnels. This allows a transitional period between on and off throttle, smoothing out the loss of downforce as the Diffuser is robbed of it's 'Sealing' skirt. Furthermore we have seen that throughout 2012 as Red Bull made revisions to the rest of their aero scheme they also changed the quantity/geometry of the Cross-Under tunnels which undoubtedly mirrors the other changes when considering centre of pressure.