ShapeNode n1 = diagram.Factory.CreateShapeNode(0, 0, 10, 10);
ShapeNode n2 = diagram.Factory.CreateShapeNode(60, 0, 10, 10);
MyLink link = new MyLink(diagram, n1, n2);
diagram.Links.Add(link);
link.Text = "test";

public class MyMyLink : DiagramLink
{
	public MyMyLink(Diagram d, DiagramNode n1, DiagramNode n2) : base(d, n1, n2)
	{
	}
}

public class MyLink : MyMyLink
{
	public MyLink(Diagram d, DiagramNode n1, DiagramNode n2) : base(d, n1, n2)
	{
	}
} 

shows the text in my test app. The "nothing here" comment cannot be true since you must create at least a constructor to pass arguments to the base DiagramLink constructor. If you are overriding the Draw method, make sure you are also calling base.Draw or otherwise you will have to render the text yourself by calling Graphics.DrawString(). Also make sure TextColor is not set to Color.Empty or Color.Transparent.

I hope that helps,
Stoyan

Yes, they are equivalent.