The magic number for online retail sales in the U.S. this holiday season is $44.7 billion, according to a report released this week from Forrester Research Inc.

"The growth rate represents an increase from 2008, when, on the heels of the worst of the global financial crisis, online holiday retail sales in the US grew just five percent," the release said.

The conclusion drawn by Forrester officials: Online sales is the growth engine for the retail industry.

That may not be new, since it's grown year-over-year for some time (though 2007's 20 percent was unusually high). But this year's projected leap is significant, especially in light of other retail projections that call for flat growth among stores.

The numbers may raise questions and concerns for local retailers, too, since part of their mission is to convince shoppers to spend money locally.

Data from the 3/50 Project - as mentioned in a recent AnnArbor.com article on local shopping during the holidays - offers some data to help people concerned about buying locally.

"For every $100 spent in locally owned independent stores, $68 returns to the commuity through taxes, payroll, and other expenditures. If you spend that in a national chain, only $43 stays here. Spend it online and nothing comes home."

Meanwhile, a local online marketer says e-commerce sites will "go back to basics" and not rely as much on social media sites this season. We reported that on this site on Tuesday.

Forrester defines the holiday shopping season as the months of November and December. Read the company's press release here.