>Whoops - I just happened to notice it haven't tried it (don't they test their sample code ? or have I just answered my own question ? ). While I have your ear do you know of any good sources of info for creating custom class designers ? e.g. adding ones own custom tabpages to a custom tabcontrol at design time ?

You mean something like this?

using System;
using System.Drawing;
using System.Windows.Forms;

public class myForm : Form
{
    private TabControl myTabControl;
    private Button cmdAddPage;

    public myForm()
    {
        this.myTabControl = new TabControl();
        this.myTabControl.Location = new Point(25, 25);
        this.myTabControl.Size = new Size(250, 250);
        this.ClientSize = new Size(300, 350);
        this.cmdAddPage = new Button();

        this.cmdAddPage.Location = new Point(25,280);
        this.cmdAddPage.Text = "Add a page";
        this.cmdAddPage.Click += delegate { AddTabPage(); };
        this.Controls.Add(myTabControl);
        this.Controls.Add(cmdAddPage);
    }

   private void AddTabPage()
   {
        TabPage pg = new TabPage( );
        myTabControl.TabPages.Add( pg );
        pg.Text = String.Format("Tab page#{0}",myTabControl.TabPages.Count);

       Label lbl = new Label();
       TextBox tb  = new TextBox();

       pg.Controls.AddRange( new Control[] {lbl, tb});

       lbl.Text = ((Control)lbl).Parent.Text;
       lbl.Location = new Point(10,10);
       lbl.Size = new Size(100,20);

       tb.Location = new Point(110,10);
       tb.Size = new Size(100,20);
    }

    static void Main()
    {
 Application.EnableVisualStyles() ;     
 Application.Run(new myForm());
    }
}

Oh you were talking about design time. I'm not good with designers and more code oriented.
Cetin