I'm copying this from the BB at work. Snopes says it's true.
http://www.snopes.com/fraud/sales/giftcard.asp
Just a little warning before traditional gift giving time.

Well the crooks have found a way to rob you of your gift card balance. If you buy Gift Cards from a display rack that has various store cards you may become a victim of theft. Crooks are now jotting down the card numbers in the store and then wait a few days and call to see how much of a balance THEY have on the card. Once they find the card is "activated", and then they go online and start shopping. You may want to purchase your card from a customer service person, where they do not have the Gift Cards viewable to the public. Please share this with all your family and friends...