Hi,
Actually, a few of us here are working on that problem.
We have considered a number of alternatives ranging from
biologically inspired spring flexures with mechanical storage
(ie. latches) mechanisms to buckling of beams and plates to
electrostatic repulsion from dielectrics.

To start with, you'll find that standard substrates (like single
crystal silicon) have sufficient maximum energy densities to
propel chiplets quiet some distance.  The main difficulty seems
getting that energy in there (ie. how do I load my spring with that
much energy without some titanic, power-hungry actuator).  That's
one of the things insects do incredibly well.  James McKlurkin is
the guy to ask about these wonderful biological mechanisms.
Aside from those, we're looking for other neat ways to have these
guys hop or tumble.

I'm glad someone else wonders these about these little things!
michel maharbiz