Exhaust blown diffusers were out-lawed a while ago in F1, but a lot of that down-force has been regained through the clever shaping of sidepods, exhaust exits. inner-wheel vanes and the resultant coanda & downwash effects. Scarb's blog article on it is well worth the read if you like this sort of technical stuff.
Quote from: Scarb's F1Coanda â€" The tendency of a gas or liquid coming out of a jet to travel close to the wall contour, even if the wall’s direction of curvature is away from the jet’s axis.
http://scarbsf1.com/blog1/2012/10/15/analysis-coanda-exhausts