They were talking about stored-value cards, such might be used by schools for children to pay for their lunch, or store 'gift cards'. The way their system works (or the one they were talking about at the event) is that the credit on the card is stored on a central database, and, when the card is used for payment, the payment terminal communicates with the central database to check for available balance and deduct value as appropriate.
A couple of thoughts:
1) One of the virtues of the system - as presented by epay - is that it tracks use of the card. The central database 'knows' where and when the card is used. You wouldn't necessarily realise that, I'd not thought about it for store gift cards anyway. I'd thought of them as like cash, with the value 'on' the card, and therefore essentially untraceable. Of course a gift card can be passed between people (given as gift!) and you are not tracking who is using it, so it's not tracking you like a credit or debit card does, but even so it's not as anonymous as cash. Sometimes I like being anonymous (even though, pace Paul McMullan, I'm not a paedophile*)
2) But more relevant to the exploration of the nature of information, it draws attention to the problem of locating information. I thought the information was on the card, but it's not, it is on the database. But actually epay have more than one database. The main database is in Germany, then they have a mirror in the UK. So is the information on the German database or the one in the UK? And presumably they have a backup, so that if the database crashes it can be recovered.
There's nothing special about this, about stored value cards. Similar things can be said about, for example, the text I'm typing on my PC at the moment. Where is it? Is it on my computer, or on one of Google's computers somewhere? It's just that the stored-value card brought the question into sharp relief, because you might think the information is on the card (well I thought it was).
But even with cash when you start to think more carefully it's not so clear where the information is. Information is money but a five-pound note (or a pound coin) is only any use by virtue of its relationship to the monetary system in which is resides. This is reminder that information might have a body, but it doesn't reside in the body (think about Katherine Hales).
As an aside, not all card payment systems work in this way. Some use smart cards which store information on them. Apparently the Oyster cards used on the London underground are smart cards which keep track of the credit on the card. There is a central database, however, and the Oyster card terminals communicate with the central database which is updated overnight. (Thanks to one of the epay people at Digital by Default for explaining this. epay don't run the Oyster card system but he knew how it worked.)
* Paul McMullan, former deputy features editor of the News of the World. Actually he was referring to privacy, but it's the same idea. McMullan's evidence to the Leveson inquiry (from the Guardian live blog, Tuesday 29 November 2011):
McMullan is asked to clarify whether he believes that no one should have privacy. He says "yes".