Total trust in them. Again its totally the media blowing things out of proportion. Granted there was a massive risk but was anything really confirmed about actual details been stolen other than the hackers had access?
Sony did the right thing shutting down psn for a while, i think everyones over it or should be over it. I have used a psn card the other month but i added funds the other day using my card. Perhaps it is stupid of me but i really think the chances of any of your card details been taken and used for fraud, are as high or as equal to as say shopping on Amazon.
Do you go out and buy gift cards for online retailers every time you want to purchase something? If you do purchase cards for PSN for that reason, why not any where else? What makes you think that its safer to use your card anywhere on the internet?
Its usually pretty safe, but there are risks involved as with anything, but to be fair there more positive outcomes than there are negatives when it comes to using cards on the internet. Just keep track of your statements, notice anything odd, contact your bank, simple.