It was already broken before Christmas, I happened to go on their site the day before and even a simple search failed, category pages didn't load in a timely way and things were just visibly bad... As they have been for so long. Months ago we had a click-frenzy promotion, an attempt to have an Australian black-Friday situation and a number of web sites failed in the deluge of visitors, including at that time.. Myer.
This is a systemic problem and as a web tester I have a fair idea what is going on. The system selected and used for e-commerce is slow, the amount of legacy systems it links to and depends on is huge and when under pressure it will fail. It's not a matter of fixing it or simply throwing more technology at it, this will in fact make it worse. They don't penetration test, they are not secure, they are not up to the task of handling decent (and expected) consumer clicks and traffic, they will continue to waste money and prestige going down this path. This is another healthcare.org
Companies such as Myer here in Australia are complaining about their online competition and that they are losing sales to this new opportunity, other companies are making successful inroads into the sales market here because their sites work and provide a solution to consumer demand, the Australian retail and department store logic is to provide an over-priced and costly system that fails, reduce sales and support staff in the stores and then complain to the government that they have no protection against this competition.