I have no experience with game cards but wanted to add something anyway:
After a friend of mine had his account hacked (trojan keylogger, of course), they used the attached credit card to purchase all kinds of premium services before transferring all the assets of his characters to someone in *some goldselling country*. After much anguish and effort, the account, characters, and assets were all recovered and restored. It's part of life these days in MMOs but there is an interesting lesson here. Even if you subscribe on a recurring subscription plan with a credit card, you are better protected if you enter your subscription term, let it charge your card, then delete the credit card (edit: as a payment source, not the card itself) and cancel your "recurring" subscription immediately. Your subscription will last the full term you paid for, your credit card is not stored and can't be used or obtained by hackers. When your term expires, it is pretty simple to enter your card info in again and resubscribe if you wish to.
Edited, Dec 11th 2011 10:02am by Samatman
____________________________Samatman 70 Shadowknight - Innoruuk
Samatman 85 Death Knight - Silver Hand
Samatman 19 Rogue / 14 Scholar - Runnyeye
Samatman 10 Champion - Brandywine (LoTR beta)
Samatman 7 Wrathguard - Dorzhan