None, and I don't plan on doing so.
To all the people that hate cash cards and those that buy them... why? Quit manipulating the situation to make it look silly by saying things like, "Wow buying fake money in a game its just pixels lel lozer." It's not exactly about what one actually purchases, it's about what the purchase will do for one and what benefits it has. Obviously a player who buys a cash card gives a monetary value to a) the time saved "working" for the money, and b) the increased enjoyment of the Online that is enabled through increased spending power.
Personally, I don't think cash cards are worth it because GTA:O, to me, isn't dictated by my money. I don't really care about how much cash I have (though I do like hovering around $100,000); I play casually and it's more about just doing something with my friends as we laugh over the phone or mic. But that's just me. Others want a Buzzard, want the highest-end super, want the notorious Rhino as soon as they can, so they buy cash cards to help them further enjoy the game.
Even the argument about how the game is catered to purchasing the Shark Cards is invalid. GTA:O is an RPG, and it's supposed to take time to make it to the big leagues. That's how the game works. Getting $100,000 for delivering a car to Simeon would be ridiculous, money would be too easy to get, and the game would quickly get boring. As you play more, the more and faster you can make money. Why? It's an RPG. One thing I do think Rockstar should add, though, is a mode similar to GTA IV online, which has no money.
What they do with their cash isn't up to you to judge. Seriously, you should be grateful they're keeping the DLCs free.