For Luke Knowles and Simon Jobman, the rising popularity of online shopping made them wonder if anyone could create such a “holiday.” Less than three weeks later, they did – though with Free Shipping Day, Knowles and Johnson also hoped to inspire a new best-selling day, rather than just note one.

Even with such short notice, over 250 merchants agreed to present free shipping offers yesterday, Dec. 18. For some smaller merchants, their participation resulted in traffic to their Web sites at record levels, according to Knowles, founder and CEO of FreeShipping.org .

"I just wanted to let you know that we had our highest visitors ever on the site yesterday which resulted in great online sales as well,” Kari Kraichely, owner of Charm Boutique , wrote in an e-mail to Knowles.

Both Knowles and Jobman hoped that the “holiday” would extend a online shopping season that traditionally fades after Dec. 10, once consumers fear they will not receive their gifts by Christmas Eve.

“Retailers really grabbed on to that vision and saw that this could be really useful, that this could be helpful, that this could create some publicity – especially this year, with the economy,” Jobman said.

As comScore noted in a study released Wednesday, a “clear correlation” exists between online retailers’ use of free shipping and dollars spent per order. After the two weeks including Black Friday and Cyber Monday offers, retailers that cut back on free shipping deals saw their average order values decline.

As for the rest of the season, “it’s possible that the strong promotion of this free shipping day may help keep consumers spending online in the season than they normally would,” said Andrew Lipsman, senior analyst, in an e-mail.

Given the surprising results he has seen, Knowles is already anticipating next year’s “holiday.” As early as next month, he plans to consult merchants on when the next Free Shipping Day should take place.

“Next year we want there to be 500, 750 – 1,000 retailers take part and have this be even bigger,” he said.