I bought a Cirkut #10 in July 2008, from Kenneth Snelson. It came well reccomended by at least a couple people here on this site. I've shot about 8-10 images with it, including one at a motorcycle rally in Duluth MN with about 1,000 people in the image. Setting up and shooting such a scene is one of the most amazing photographic experiences I've had in my life, combining drafting and composition and photography skills all into one. Also coaching skills, as I had 3 assistants for that shot, and basically coached them an hour ahead of time, and laid out the shot, as we had just 15 minutes to get all the people into place at 4:00 PM.
Here's a rough pic of the result. The colored version is several d*g* images, stitched; b/w is Cirkut:
And here's the very cool sales pitch from the Aerostich catalog:
I'm a newbie at Cirkut stuff, so at this point that's the climax of my Cirkut experience. But had been reading about the subject for a couple years before buying one. Seems to me there's about 1-2 Cirkut photogs using them in states east of the Mississippi, and fewer than that in states west of the Mississippi. But that's just a guesstimate on my part.