I hate when I get prepaid cards, the things are just evil
They do have their uses, though. As one of the few online payment methods that are practically untraceable*, they're handy if you want to make an anonymous transaction (admittedly, that's not something that comes up often

). Also good if you're suspicious of the business you're buying from, but have no alternatives (Origin, for example).
*if you pay for it with real cash, 'bout the most they can do is figure out where you bought it and try for CCTV footage... which would take effort and be fairly easy to stymie.