Photoshop CS4's new GPU-aware nature allows it to share intensive tasks with the graphics card, speeding up operations significantly. Photoshop will offload panning, zooming, canvas rotation and several other operations to the GPU, allowing users to also experience a more free-flowing workspace.
I received some movies from NVIDIA demonstrating the new GPU accelerated features. I copressed them into one big 50 MB archive, feel free to download and have a look. Looks pretty impressive really.