The Triple-Action is generally the same as the Dual-Action, but adds an "up & down" motion to the equation.   There is spring tension pulling the auger down and as it turns, allowing the auger to "climb" the clothes or what ever (bulky items?) you are washing as it rotates.   I believe this is supposed to help "pull" the items down as well.   Either that or it's supposed to have a more gentle "pull" on the clothes?   (I'm not too sure about the last part)

You can see what I mean by grasping the auger and pulling it straight up.   It should move about 1/2 - 3/4 inch, if memory serves.

Though you really can't tell in the photo, this is a "Triple-Action" in my KM Elite Catalyst washer.

Kevin 

I've always felt that while the dual action agitator is a great concept, it is not that effective in practice. It needs bigger vanes! Like 2 or 3 times as wide, now that would be cool. When watching one operate I always am thinking of better ideas. How could you get the auger to move continuously in one direction rather than in a jerky ratcheting motion? The idea I came up with is to have a little motor built into the lid that ran while the machine was in operation and attached to the top of the agitator. Biggest drawback in my design is that you would have to have the lid closed while the machine was running