Overall though its nice to see a non jQuery plugin! And it's very nicely done.

Could use some finessing, on Opera there appears to be a white square/rectangle that appears on the next element for the second and third ones (not sure why). Then it disappears. Maybe it's an Opera thing.

The styles that get applied to the element inside of the "white box" get applied before the white box moves. This is noticeable for the links in the top right. They turn light blue before the box even moves. It should be after the box has moved, since that kind of stuff is pretty much instant.