I have just been testing Apple's new Mac Mini with Catalyst Xpress (finally got my hands on one).
It works!
I have been testing with DV PAL and DV NTSC footage. The Mac Mini I have using is the higher spec'ed 1.42GHz machine, using an external, powered, 7,200 rpm firewire drive.
At 1024 x 768@75Hz, I got two DV PAL movies + mask at 25fps
At 800 x 600@60Hz I got two DV NTSC movies + mask at 30fps.
The colour and visual effects appear to work as designed.

Obviously the Mac Mini is not a G5 tower, but it's very interesting for a low-end Catalyst Xpress system.

Hugh
Catalyst Test Bloke.