Okay, so we all know retailers are looking for every holiday edge this holiday season. Consumer spending's been down, and the sprint to Christmas offers the last chance to pump up those Q4 numbers. They are trying out new ways to reach and engage shoppers, particularly via social media. But, the most effective way to bring new customers into the fold -- and keep them around for a while -- may be to pick up the shipping tab. It's pretty old fashioned, but it's best by test.

Once considered a bonus, a special effort, free shipping isn't really optional any more. If a shopper has to pay for shipping from one retailer, he may move on, knowing that plenty of others aren't charging for it. Rebecca Lieb, vice president at Econsultancy, a digital marketing news publisher, notes, "You're delighted the first time you get free shipping, but you expect it the second time."

And, free shipping shouldn't come with any strings attached, according to Shop.org's eHoliday Study (Shop.org is the e-commerce division of the National Retail Federation). Five years ago, 25% of retailers didn't charge for shipping during the busiest shopping day of the year. This year, however, 57% are planning not to hit their customers up for the extra cash, making this cost just another expense associated with running the business during the holiday season.