If you read "Kingpin", even though the owner of one of the top carding forums could have just traded digital goods and been fine, he choose to dabble in physical goods for the money/whatever. That was how he was caught. I'd surmise the predators are not too different, though perhaps decidedly more cautious.
It's where people (think mostly the lowest common denominator of wannabe hackers like script kiddies and such, i.e. not just bad but fairly inept) go to learn how to and share information about stealing credit card information, usually leading to minor levels of success if they keep at it, it seems.
