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And, of course, another reason foot traffic was down at brick-and-mortar stores is because online sales were up--way up. The second week of December, from the 10th to the 16th, broke records to become the first $7 billion week in online history.

Typically, online sales begin to dwindle in mid to late December as last-minute shoppers tend to favor brick-and-mortar buys to costly expedited shipping fees. But not this year. Thanks to Free Shipping Day on December 17th, and innovative methods from retailers like eBay's Holiday Express, which provides product delivery in as little as one hour after a mobile purchase is made, online sales were up 52.8 percent from the corresponding period last year. Free Shipping Day raked in a whopping $1 billion alone, while the five day work week period from December 17th to December 21st hit $3.69 billion.

Mobile sales were also through the roof. Sunday December 9, which is apparently “Mobile Sunday," was the heaviest mobile shopping day, with both eBay and PayPal hitting record daily highs in mobile volume--higher even than Cyber Monday.

There's no doubt that it's a brave new world when it comes to how consumers shopped this holiday season--the one question that remains, though, is how retailers will adapt.