Apart from providing you with a performance boost in Adobe's professional video software, such as Premiere, Photoshop and After Effects, regular business users will also benefit from ATI hardware.
Acrobat 9 Pro can already utilize the awesome might of HD 4000 and HD 3000 cards. We didn't have the time to try it out, opening PDFs shouldn't be much of a problem without hardware acceleration, but creating and converting them is a different story altogether.
You can try it out by checking the “Use 2D GPU acceleration” in the Edit -> Preferences -> Page Display tab and let us know if it's faster on ATI or not. Maybe this might work on Nvidia as well, as this feature should be using either OpenGL or Direct 3D instructions and it should work on both cards.