Eddie Gunks recently uploaded a video on Grafmatic holders to YouTube. As far as I can tell, it is the only video on the internet that demonstrates how these holders work. I expect to receive a Grafmatic holder in the next few days and found the video quite helpful. I thought that I'd flag it here, both because it is useful and to ensure that a search on this site for info on Grafmatics will pick up that there is a good video on their operation.
The long version of the video is at http://www.youtube.com/user/eddiegun...19/xIY5X6-l0tw
There is also a short version: http://www.youtube.com/user/eddiegun...15/0TSATdotG1Q