There is a specific FAQ about it here:
http://www.iagshares.com/phoenix.zht...shareholderfaq
Shareholder discount scheme
Former individual British Airways shareholders are eligible for a discount on certain British Airways flights if they hold more than 200 British Airways ordinary shares. There is no equivalent scheme for former Iberia shareholders. It is expected that IAG will implement a shareholder discount scheme and shareholders will be provided with more information in due course.
Former eligible BA shareholders continue to receive a 10 per cent discount on-line on flights for bookings made during 2011*