I watched this video at Youtube and it was tagged as a failure, but I think it is pretty impressive to see the cheetah getting up from the floor.
And although it goes down when the center of gravity moves forward I agree with some of the comments on the video about either trying to move it back or to add more weight on the back part.
Watch it in action.
You can see more photos and info at http://www.eurobricks.com/forum/index.php?showtopic=52997