Rear & Diffuser:
1) Flow director/deflector to aid rear wing effectivness
2) Rear wing twin splitter to aid flow of air thrugh the rear wing
3) Low directional exausts, quickest way to get rid of gases, may not be aero efficient
4) Diffuser of RA108, less effective that number 6
5) Louvers or shark gills, aids cooling (Illegal as of 2009)
6) Spoon or Dboule Deck Difuser (DDD), therefor the loss of overall loss of downforce on 2007 levels is arround 35% at maximum, most likley arround the 20% mark. Worth arround 5% of overall performance of the car, taking 1% as 0.1 of a second, thats worth arround .5 a second a lap, more likely arround the .7 second mark with the overall aero package in that aera of the car.
7) Covered exausts, aiming at rear wing to try and aid aero downforce with a little more downforce.
8) Extended engine cover. Guides air toward the rear better and minimises yaw at the same time, not as effective as the shark fin on the Red Bull RB5/Toro Rosso STR4/Toyota TF109/Renault R29, but still effective enough to help minimise negitive yaw.
You can also see the diffrence between the rear wings better, Wide and low of the RA108 and Tall and thin of the BGP001.