USA Today reported this web site which is a virtual trading post of various gift cards.
A quick look at the site shows that it is hardly an exchange -- you may only find one or two available gift cards for sale for each retailer, and most items are priced at around 90% of face value (some 100%), making it unlikely to be astoundingly appealing to bargain hunters.
The site makes money by "charging sellers a processing fee of 7.5% of a card's selling price." The USA Today article may bring some traffic, but I seriously doubt the survivability of this site, especially when Ebay has been maintaining the same market for quite some time, it charges less fee, and it has deeper inventory.