In some ways, it seems like Cyber Monday should have been no big deal for e-commerce this year.

Smartphones have put the Internet in our pockets, meaning there’s less need to wait until Monday morning when people return to their office computers to scope out the digital deals. Plus, holiday shoppers have already been on a digital spending tear for several days: 103 million people shopped online between Thanksgiving and Sunday, and consumers spent a record $8.03 billion online during that time period, a 17 percent increase over last year.

And yet online sales on Monday were on pace for a record-breaking day, with forecasters from Adobe projecting that $3 billion would be spent online before the deals bonanza was over. That would be the most money ever spent online in a single day, according to Adobe, whose software is used by many retailers.

Even as retailers were ringing up big online sales, the day provided ample evidence that some of them still have a long way to go to adapt to an era when more and more people are shopping from their smartphones and tablets.

Shoppers visiting Target’s website, for example, experienced delays Monday morning. Amid a crush of traffic, the retailer said it had to resort to metering activity on its site, prompting frustrated shoppers to get a message advising them to “please hold tight.”

Meanwhile, Adobe reported that as of 10 a.m., 15 out of 100 product views across the e-commerce landscape were showing an item that was out of stock. That’s about 2.5 times the normal rate, the company said, and it’s not good news that so many items were unavailable so early on in a sale. That likely means some shoppers who hit the Web later in the day came up empty, especially on certain in-demand toys (especially “Star Wars” items) and electronics.

Retailers tried to design their sales this year with an eye toward changing shopping habits. Wal-Mart, for example, started its Cyber Monday sale at 8 p.m. on Sunday after noticing in previous years that many shoppers started hunting for the deals around that time. Amazon.com, meanwhile, started its blitz of more than 30,000 “lightning deals” way back on Nov. 20, likely a nod to the fact that shoppers are looking for deals long before Cyber Monday – or even Black Friday – arrives.

Cyber Monday’s traffic and purchasing patterns underscored the extent to which the retail wars are increasingly being fought on the smallest of screens. Adobe reports that some 53 percent of traffic and 32 percent of online sales came from a mobile device. Most of that traffic was from smartphones, with a significantly smaller share coming from tablets.

The surge in online orders means that the pressure will be on retailers and shippers to get packages to shoppers in a timely fashion.

Consultancy Kurt Salmon, which works with retailers on supply chain issues, said it has found that some large retailers had trouble filling seasonal jobs in their online distribution centers this holiday season. That could suggest troubles ahead handling the deluge of orders.

As online sales surged on Cyber Monday, capping a long holiday weekend, it appears that there was less action in brick-and-mortar stores. According to RetailNext, an in-store analytics provider, traffic to physical stores was flat and sales were down 1.5 percent over the long weekend.

The strong online sales growth over the holiday weekend, did not appear to give investors confidence that retailers were in for an especially merry Christmas. The stocks of many major chains, including Macy’s, Kohl’s, Target, and Costco were down on Monday.