Update: Keyframe Animation 1.8

Version 1.8 now lets you animate the size of objects. Make them grow, shrink, or stretch them in different directions.

Any recorded change in the size of objects will be interpolated between key frames. The scaling can be uniform, or non-uniform.

You can combine a translation and a scale operation, so that the object moves and changes size at the same time. 

Rotations and scale can be combined if you rotate and scale about the same point.  (They don't have to be the same point, but if they are, then that point will remain fixed while the object is interpolated.)

The tweens have support for animating the scale of objects, so the animation can be exported to a movie.

Here is a quick demo.