Yes, I have seen those hanging systems. They do a fair job of trying to hide the systems so the artwork stands out not the hanging system. But I think the carpet on the wall idea is really neat.
I thought I would try doing a web search to see what I could find. I need to do that anyway for when I start remodlelling. Here are some interesting links I found (once I figured out a workable search term that didn't give me tons of hits for 'wall to wall carpet')
Here is a neat little 'velcro-like' hanger that will stick itself to the wall carpet:
http://www.prohanger.net/
This one takes the carpet idea and uses it for festival displays:
http://denver.craigslist.org/art/293212371.html
Here is someone who tells about installing carpet on the walls of a home theater:
http://www.fatbulldog.com/theater_complete_new3.html