My view, not dissimilar to many expressed above, it's pure hype.
It's also designed to allow retailers to shift a good chunk of 'Christmas' stock at 20% off now, rather than 50% off in Boxing Day sales, because consumers (finally) wised up to post-Xmas sales and started waiting, not buying before.
Sure, they'll be a few genuinely decent deals, but few stunning bargains, merely those needed to fuel the hype and generate the publicity.
What did I buy? I got precisely what I went looking for.