I'm looking at the CS5 page info..it states it there.
The Mercury Playback Engine doesn't just deliver blazing performance and a fluid editing experience. By more optimally using your entire system performance, it also accelerates rendering and encoding, reducing the time required to deliver content to your clients. The only thing we canít help you decide is what to do with all of the free time you'll now have.
Mercury brings performance gains on all of the GPUs supported today in CS5. If you're upgrading your system today and want to get the most out of your configuration, the following graphics cards offer significant additional acceleration by the Mercury Playback Engine:
GeForce GTX 285 (Windows and Mac OS)
Quadro FX 3800 (Windows)
Quadro FX 4800 (Windows and Mac OS)
Quadro FX 5800 (Windows)
Adobe is planning to support additional cards in the future, including some of the new NVIDIA solutions based on the upcoming Fermi parallel computing architecture.