Code

class LinkAnimator
{
	public LinkAnimator(DiagramLink link, DiagramView view)
	{
		this.link = link;
		this.view = view;
	}

	public void AnimatePath(
		int animationLength,
		params PointF[] points)
	{
		if (points.Length < 2)
			return;

		// total length of specified path
		float pathLen = Enumerable.
			Range(0, points.Length - 1).
			Aggregate(0f, (len, index) =>
				Utilities.Distance(points[index], points[index + 1]));

		// prepare the link
		link.ControlPoints.Clear();
		link.ControlPoints.Add(points[0]);
		link.ControlPoints.Add(points[0]);

		// animate from a thread
		var animationThread = new Thread(
			() =>
			{
				for (int s = 0; s < points.Length - 1; s++)
				{
					// how much to grow the segment for each animation frame
					var segment = new Vector(points[s], points[s + 1]);
					float segmentTime = animationLength * segment.Length / pathLen;
					var increment = segment * FrameLen / segmentTime;

					// frames for current segment
					for (int f = 0; f < segmentTime / FrameLen; f++)
					{
						Thread.Sleep(FrameLen);
						link.EndPoint = link.EndPoint + increment;
						view.Invoke(new Action(
							() => link.UpdateFromPoints()));
					}

					// set exact position in case animation hasn't reached it due to rounding
					if (link.EndPoint != points[s + 1])
					{
						link.EndPoint = points[s + 1];
						view.Invoke(new Action(
						    () => link.UpdateFromPoints()));
					}

					// add next point
					if (s < points.Length - 2)
						link.ControlPoints.Add(points[s + 1]);
				}
			});
		animationThread.Start();
	}

	DiagramLink link;
	DiagramView view;

	const int FrameLen = 1000 / 30; // in milliseconds
}

diagram.LinkShape = LinkShape.Polyline;

var n1 = diagram.Factory.CreateShapeNode(10, 10, 20, 20);
var n2 = diagram.Factory.CreateShapeNode(210, 10, 20, 20);

var n3 = diagram.Factory.CreateShapeNode(10, 110, 20, 20);
var n4 = diagram.Factory.CreateShapeNode(210, 110, 20, 20);

var l1 = diagram.Factory.CreateDiagramLink(n1, n2);
var l2 = diagram.Factory.CreateDiagramLink(n3, n4);

new LinkAnimator(l1, diagramView).
    AnimatePath(2000,
        l1.StartPoint,
        new PointF(70, 10),
        new PointF(130, 30),
        l1.EndPoint);
new LinkAnimator(l2, diagramView).
    AnimatePath(1000, l2.StartPoint, l2.EndPoint);