I think it is bad advice to suggest drivers use their left foot for braking. While using your left foot may be result in shorter stoppage distances in the rare case of an emergency (assuming the driver lifts on the accelerator with their right foot and applies their left foot on the brake), there are problems in not using your right foot to brake.

First, using your left foot results in frequent and often inadvertent braking, thus causing problems for those behind, particularly on the motorways. Second, I would bet a large amount of money that unintended acceleration is often because the right foot stays on the accelerator rather than being lifted and used to brake. Finally, this is not Formula 1 and the average driver, in my opinion, simply does not have the skills to operate left-foot braking.