Thanks for the description Kootenanny. There's another excellent description here, the Patman's Rekluse Clutch review on KLRWorld.com:
http://www.klrworld.com/index.php?option=com_content&task=view&id=116&Itemid=156(Scroll about halfway down the article for a section on how clutches work.)
The Rekluse clutch is pretty amazing; the way it works is via steel ball bearings that sit in grooves that are deep toward the center of the disk and shallower toward the edge.
As the plates spin up, the ball bearings roll out/up (into the shallower part of the grooves) from centripetal force, forcing the plates together. Pretty ingenious!

I'm still thinking of getting one of these. As the Patman says, the Rekluse controls the clutch better than any human ever could.

Scott