You asked for half baked ideas, but I have a couple of half frozen ideas instead.
Nano scale actuator
Because it is possible to change the temperature of nanoscale objects very quickly it should be possible to make a structure that contains H20 and cycle it from ice to water. This will create a shape change that can be the basis of a nanoscale actuator. (there is a 9% volume change when water freezes/melts.)
Using Ice to fill the negative space
I have looked at lot of 3D prototyping systems, they all have some sort of material to fill the “negative” space in object they are building which is removed later. Would it be a useful idea to assemble in an icy state then melt the ice and drain away the unwanted liquid water? The melting and flowing of water could do the jobs of final positioning and adhesion of parts nano scale and larger.