Code

private void OnNodeCreated(object sender, NodeEventArgs e)
{
    ShapeNode sNode = (ShapeNode)e.Node;
    sNode.Text = "Enter description";
}

private void diagram_EnterInplaceEditMode(object sender, InPlaceEditEventArgs e)
{
    ShapeNode sNode = (ShapeNode)e.Node;
    if (sNode.Text == "Enter description")
        sNode.Text = ""; //Remove default text
    string myTextToEdit = e.Item.GetTextToEdit(); //Here the text is removed, but in the box on the screen is the text still there
}