R600, Radeon X2900 series will have some cool video features. We already told you a bit here. When we went deeper in the stuff we've seen we learned that R600 can process two independent video streams.
The big R600 chip has a video part of chip called resource schedule that can process two independent video streams, even in High definition.
Radeon X2900 will be able to play your HD content as s first stream while you will be able to watch a second stream as a picture in picture feature. You saw this in most high quality LCD and High end TVs. This will be cool and definitely indicates that R600 unified Shaders can do more than graphics, they can take care of two HD streams.