Shopping online has many advantages. You can put on your pj's, open a bottle of wine and avoid the crowds—all while crossing items off your list.
But what happens when that convenient process is ruined by late delivery of a package, with the result being no gift under the tree?
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For the first time, StellaService, which rates retailers on customer service, scored store websites on meeting promised delivery dates for holiday orders.
On the advertised cutoff dates for standard orders to be delivered by Christmas, mystery shoppers bought one product from a group of 25 retailers (including Wal-Mart Stores, L Brands' Victoria's Secret and Amazon), sending the gifts to three locations around the United States.
Eight of the companies failed to get their products to recipients by Christmas in at least one region. Of 75 packages, nine packages—or 12 percent—missed the promised delivery. Eight of those nine late deliveries were shipped via UPS, StellaService said.
"I think that what we're seeing this year are some growing pains in e-commerce," said Ty McMahan, director of content at StellaService. "More people shopped online this year, so this is kind of the first year we're stress testing the infrastructure."
The eight that missed their delivery deadlines were Staples, Dell, Macy's, , Pottery Barn, Kohl's, Nordstrom and TigerDirect. The first seven missed in one of the three regions; TigerDirect missed on both the East and West coasts,
CNBC requested comment from each of the companies and received immediate response from Nordstrom, Macy's and Kohl's.
In an email to customers earlier this week, Nordstrom cited a UPS announcement that heavy volume would delay some deliveries. FedEx, which handled only one delivery in the survey (for Gap), said it experienced similar delays.
Nordstrom Direct President Jamie Nordstrom sent a second email from the company on Thursday, in which he confirmed all shipments were given to the retailer's shipping partners before their Christmas delivery cutoff.
"While we are dependent on our shipping partners to hold up their end of the bargain on getting your orders to you, we also realize that we are accountable for meeting your expectations and take responsibility for what happened here," he wrote.
"We realize you have many options on where to shop, and weare committed to taking the steps to improve our service and meet your expectations so that we can continually re-earn your business."
Jim Sluzewski, Macy's senior vice president of corporate communications, wrote in an email that the company is "working with FedEx and UPS to understand the situation. At this point, it appears that only a small number of Macy's deliveries were affected."
A Kohl's spokesperson also wrote in an email that only a limited number of its customers were impacted, saying they have contacted those shoppers and will fully cover the cost of all items not delivered on time.
Later in the day, Gap also apologized for inconveniencing shoppers, saying it has been working with them to ensure their orders are fulfilled.
"Providing a high quality of service to online shoppers is a top priority for Gap Inc.," the statement said.
StellaService's McMahan and Kevon Hills, director of research, said earlier that they were surprised by the list, as Macy's and Nordstrom in particular have well-regarded online operations.
"Nordstrom was pretty proactive in getting out there and telling customers that this was going to be delayed," Hills said, referring to the first email the company sent to customers about the potential for untimely shipments. "If there's any silver lining ... at least they came to the customer and said, 'Hey, there's a problem, and we're going to do our best to get it to you as soon as possible.' "
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Still, most retailers tested—including , and —came through. Hills and McMahan pointed out Zappos for excellent service this holiday season. In some cases, it upgraded its shipping method to make sure packages got to their destination on time.
"Zappos is one of those companies that's obsessed with service," McMahan said, adding that it was one of three to post the latest cutoff date, Dec. 23. "They really made it a priority to let people ship as late as they can."
Although retailers who missed delivery deadlines can put some of the blame on carriers, the results could put them in a precarious position in a holiday season in which a record number of shoppers bought presents on the Internet.
According to the National Retail Federation's Shop.org, online sales are projected to increase between 13 percent and 15 percent this holiday season, for a total of more than 365 million packages sent.
Forrester Research projects that the holiday season will generate $78.7 billion in online retail sales in the United States.
If consumers can't rely on a certain store for timely delivery, that retailer could miss out on sales, according to experts.
Anne Zybowski, vice president at Kantar Retail, said that online shoppers are concerned about receiving orders in time, which often means they won't risk ordering from a store they've never purchased from before.
"All e-commerce players are not equal," she said.
(Read more: Bought a gift online? Good luck returning it)
It will be interesting to see which retailers advance their shipping deadlines next season, trying to achieve a balance between snagging a competitive advantage and fulfilling promises, McMahan said.
One definite area for improvement is flip-flopping on dates, which confuses customers, he added.
, Pottery Barn and TigerDirect changed their cutoffs for standard shipping, with TigerDirect switching from the 20th to the 18th, then back to the 20th.
"That's one thing that retailers could probably get better [at] next year," he said. "Pick a date, make that date really easy to find on the website, and stick to it."
—By CNBC's Krystina Gustafson. Follow her on Twitter @KrystinaGustafs.
(CORRECTION: An earlier version of this story misstated the number of late packages shipped via UPS. Of 75 packages in the StellaService test, nine packages—or 12 percent—missed the promised delivery. Eight of those nine late deliveries were shipped via UPS, StellaService said.)