It seems that the recent update to OSX (10.4.7) broke Canon's Camera Window software. While there doesn't seem to be an official fix for this at the moment I've found a work around which is almost as good. Plug the CF card into a normal USB card reader, the Camera Window software seems to recognise it as if you had plugged in your camera. After all the camera is probably only acting as a USB storage device anyway.
Hopefully Canon will fix this soon, I don't think it's a problem with OSX as such.