Yeah, they are fascinating and probably would be fun to fiddle with. But I have lingering doubts about the practicality of proas for the average sailor. That is a neat website, though.
On a note related to the OP's Crab Claw rig inquirey, you might take a look here:
http://www.shellboats.com/ ;
and, specifically, here:
http://www.shellboats.com/sbcrabclawcat.html
Also, there is a nice little article in the Dec. 1, 2007 issue of Messing About In Boats (p.28) in which that CrabClawCat figures prominently.