Consumers like gift cards because they make the joys of obligatory generosity easier and thus more joyous. A recent survey noted that 80% of shoppers said they were going to purchase a gift card this holiday season, for an estimated total of $27.8 billion. Companies like them too, because companies like free money. According to the Wall Street Journal, from 2005 to the present, $41 billion worth of money on gift cards has been lost or will never be redeemed. This doesn't include any of the $800 billion cost of Iraq War that President Bush attempted to pay for with old gift cards to Applebee's.
Much of that $41 billion total came from fees and expiration dates, which were removed thanks to the Credit CARD Act of 2009. But companies are still allowed to declare lost cards as income if they reasonably conclude that the gift amounts won't be redeemed. For Best Buy, that's two years. That Sock of the Month Club membership is looking pretty sweet right now.
But if you know you won't use that gift card to Build-A-Bear, you can sell it at Plastic Jungle, or one of the other sites that will pay around 80% or more of the card's value. If you enjoy wringing the slightest amount of happiness out of every transaction in your life, you can also invest in a mutual fund with a gift card on GoalMine.com, where they accept increments as small as $25.
You can always donate your gift cards to charities and schools, but you'll probably use that baby as soon as you think of something you want in a few years.