Black Friday: a tradition for many of us, and a perverse curiosity for the rest. Ultimately, though, it's an interesting bellwether of what's going on in the U.S. economy. Here's what we learned this year:

1. Online sales up ... sites weren't (always).

This year, sales from ecommerce hit a record-breaking $3 billion. The fact that sales were pretty significant shouldn't be a surprise to anyone, but yet they did manage to catch some retailers by surprise. To be fair, this happens every year. In 2014, it was Best Buy; last year, Target and Neiman Marcus experienced issues. This year, Macy's fell culprit; during the mid-part of the day, site visitors were greeted with a "temporary shopping jam!" message, leaving many irate complaints on Twitter.

Lesson to be learned: if you're an ecommerce retailer, make sure to stress test your website to the extreme. It's far better to invest in testing than to lose hundreds or thousands of transactions, wouldn't you agree?

2. Mobile is the real deal.

Not to be outdone, mobile sales surpassed $1 billion. To put that in perspective, it was the first day in the history of U.S. retail where mobile sales beat $1 billion. That's further evidence that transacting via simpler interfaces optimized for mobile is what customers want for just about every product category.

3. Cyber Monday is an outdated term.

Amazon reported that it has more mobile sales on Thanksgiving 2016 than on Cyber Monday of last year. Why? Because consumers don't care about silly, opportunistic mini-event names like "Cyber Monday" if they can get similarly good deals on other days in November.

That's not to say sales won't come in on Cyber Monday; far from it. Adobe Digital Insights' principal analyst and director Tamara Gaffney expects online sales to hit $3.36 billion on Monday, making it the largest online sales ever.

4. Where do tablets fit in?

Most mobile traffic on Black Friday stemmed from smartphones; 56% of all traffic, to be exact. However, 47% of the overall total came from smartphones, with only 9% coming from tablets. In terms of sales, only 11% of the total came from tablets.

Given that app and website developers have been developing tablet-rich interfaces for years, there's an honest question about how much time anyone should really be spending optimizing for tablets, if they're not making up a good chunk of the sales pie.

5. Sales up; backlash up too.

While millions of Americans hit the mall, plenty more went for the #OptOutside for the second year in a row. The campaign, launched by outdoor retailer REI last year, saw approximately 2.7 million consumers pledge to participate, taking advantage of free rides to parks in five cities as well as free park admission in 13 different states. REI's practicing what it preaches, giving roughly 12,000 staffers the day off for free so they could #OptOutside as well.