Here is a video clip from some Japanese show showing a Chimpanzee riding on a Segway. I'm not sure of everything that went on behind the scenes, but it looks like after watching the person ride around on the Segway and a few trial runs, the Chimpanzee seemed to get the hang of it.
The Japanese audience seems to think it is a riot watching the little guy race around on the Segway (really - it is hilarious

), but I think this says something to the intuitive control of the Segway. Dean Kamen said he wanted the Segway to be as easy and intuitive to a user as walking - I think this clip reinforces that is the case.
http://www.youtube.com/watch?v=5pFv8CAniYQ