“Spherical robots are currently in use for research, fun and even surveillance purposes. Without legs they are inherently stable and capable of traveling great distances in short periods of time. Here are five of the craziest rounded robots rolling their way across Earth.”
Spherical designs also necessarily tend to be light, and to distribute what weight they do have over a relatively large area, meaning that they have low-pressure footprints. This makes them good candidates for what I call "locally supported" devices in a recent blog post http://cultibotics.blogspot.com/2013/05/design-options-and-factors-which.html .
See on gigaom.com