private void flyMachines_NodeChange(object sender, NodeBase node)
{
    int rowCount = 0;
    try
    {
      foreach (NodeBase nb in flyMachines.Rows.Items)
      {
         if (nb.VisibleInView)
            rowCount++;
      }

      this.tsslRows.Text = _statusRows + rowCount.ToString();
    }
    catch { }
}

[c#]
private int GetFilteredNodeCount(FlyGrid flyGrid, NodeBase node)
{
  return flyGrid.ActivePort.RowCount;//when you don't use nesting
  /*-------OR-------*/
  //we need to get the viewport associated with the node
  FlyGridViewPort port = flyGrid.GetPort(node);
  return (port != null) ? port.RowCount : 0;
}