In anticipation of the Redstone Update, I've been experimenting with this type of "wormhead" piston configuration lately:
where P = normal piston, S = sticky piston, X = anything .
By alternating power to the two pistons at the extremes, one can move the entire chain in the given direction. A usage of example would be a cane farm like this one:
or an extendable fence.
This type of configuration will become more useful with the next update (hoppers allow continuous collection of items, redstone blocks allow easier movement in two dimensions).
I don't recall this type of mechanism described anywhere I read (including the Wiki), but as this is basically an extension of the self-propelling piston concept, I doubt that there isn't already a name for it. So, what is the popular name of this type of contraption?