One of the biggest changes to Premiere Pro in the new version is a renderless timeline which supports OpenCL capable graphics cards. Previously Adobe only supported NVidia’s CUDA standard for GPU acceleration. Mac users with ATI cards missed out on the huge performance gains from a GPU accelerated video editing package.
Previously even MacBook Pro users with high end (for the time) CUDA capable NVidia graphics found themselves without quite enough video RAM and in need of a hack to get it to work.
That has all changed with CS6.