Cake Poker has just established a player-to-player marketplace where participants can buy and sell Gold Cards (i.e. “collectible rewards that are randomly distributed to players at all of our real money ring games”).
If you have a spare one, you can sell it for cash in The Exchange and if you happen to need any to enter a certain Gold Card tournament, you might find one available for purchase. In order to be able to access The Exchange, an upgrade to Cake 2.0 is going to be necessary, if you have missed it yet. Once logged in, you will see the "Exchange" button in the Gold Card tournament lobby, which takes you to the marketplace.
The question arises: what is this good for? Well, apart from the obvious advantage of gaining access to these tourneys, Cake also hints that “with strategic buying and selling, you will find it’s possible to make money on Cake without ever playing a hand.”
For more details, visit their official site here.