You'll get a better idea by watching the video below of how it works.
As you can see, its a bit like a Segway but unlike a Segway, the U3-X can move in all directions just by leaning ones body weight.
The U3-X weighs under 10kg and dimensions are 315×160×650mm. Battery lasts for about an hour before you need to carry it ^^; Speed goes up to 6km/hour.
Details at Honda HP show how thw U3-X uses balancing technology used in ASIMO.
ASIMO balancing technology in action below.
Photos from Livedoor.