CoyoteBreath, you really have taken my breath away! "It's a short step from chipping a child to chipping us all"? You must have the longest legs known to man in that case, to make that a short step!
Back on cards: Sure, Tescos have a file on me, tracing what I buy. Know what? It means I get money-off coupons for things I like, like my favourite brand of crisps (chips to US folks :-) or chocolate muffins, and not for stuff like cat-food which would be no use at all. As far as I'm concerned, that's a good thing, bcos it saves me money. If you prefer to pay more for the same stuff, that's your prerogative, but please don't try to persuade me to do the same.
Security-wise, I see no problem at all. So someone could find my name from this? Big deal! Ppl can also find my name by checking on Mudcat, SourceForge, my EZBoard electronics forum, the Everyday Practical Electronics forum, etc. Or they could come up to me and ask, and I'd tell them. And if anyone can come up with a reason why I should be worried about someone knowing what food I like, I would be very interested to hear it. So far, the best argument I've heard for not signing up to store cards is "well, if you go out and hold up a bank and then say you were shopping instead, it might harm your defence"...
To get this in perspective, I suggest that you look at the Mudcat membership form which every single one of you, bar NONE, has filled in. Compulsory details are your full name and a valid email address. From the email address (for a suitably diligent searcher) can be found your IP address, which by tracing the ISP will show which area you live in. Optional but recommended details are your address and telephone number, so all that effort can be bypassed. "But we all trust Max, so it's different!" Obviously, but riddle me this - who do you think would cave the quickest to a lawsuit from some random individual, Max (who can't afford a top-flight lawyer) or a supermarket chain (which has a zillion lawyers at the press of a button)?
Please can people get their collective underwear unwedged?