SM 3.0 and SM 2.0x are now enabled by default when graphics settings are set to ‘Very High’. To see performance increases you must have Direct X 9.0c installed.
This is from patch 1.3 change log, HOWEVER, I MOST CERTAINLY WASN'T RUNNING ANYTHING IN 'VERY HIGH' QUALITY before forcing PS1.4
I tried running in 'Very High', high or medium, and I swear, forcing (PS1.4 made 'Very High') smoother than (medium with PS2.0).
I KNOW I'm loosing some effects, but what counts stayed: Heat Haze, reflections, normal mapping etc...