How to move a Windows Form when its FormBorderStyle property is set to None?

Here it is the best way I have found. It is a ".NET way", wihout using WndProc. You just have to handle the MouseDown, MouseMove and MouseUp events of the surfaces you want to be draggable.

private bool dragging = false;
private Point dragCursorPoint;
private Point dragFormPoint;

private void FormMain_MouseDown(object sender, MouseEventArgs e)
{
    dragging = true;
    dragCursorPoint = Cursor.Position;
    dragFormPoint = this.Location;
}

private void FormMain_MouseMove(object sender, MouseEventArgs e)
{
    if (dragging)
    {
        Point dif = Point.Subtract(Cursor.Position, new Size(dragCursorPoint));
        this.Location = Point.Add(dragFormPoint, new Size(dif));
    }
}

private void FormMain_MouseUp(object sender, MouseEventArgs e)
{
    dragging = false;
}

I know this question is over a year old, but I was searching trying to remember how I've done it in the past. So for anyone else's reference, the quickest and less complex way then the above link is to override the WndProc function.

/*
Constants in Windows API
0x84 = WM_NCHITTEST - Mouse Capture Test
0x1 = HTCLIENT - Application Client Area
0x2 = HTCAPTION - Application Title Bar

This function intercepts all the commands sent to the application. 
It checks to see of the message is a mouse click in the application. 
It passes the action to the base action by default. It reassigns 
the action to the title bar if it occured in the client area
to allow the drag and move behavior.
*/

protected override void WndProc(ref Message m)
{
    switch(m.Msg)
    {
        case 0x84:
            base.WndProc(ref m);
            if ((int)m.Result == 0x1)
                m.Result = (IntPtr)0x2;
            return;
    }

    base.WndProc(ref m);
}

This will allow any form to be moved by clicking and dragging within the client area.