Well, if you buy "Honey Bunches of Oats" in Store A and then "Dannon Lite n' Fit Yogurt" in Store B, "they" can piece together some details of your route. If you got between them too quickly, an AI system can send you a speeding ticket automatically. If there was a hit-n-run on the projected route between the store(s) and your house around the time you would have been driving there, you're on the suspects list. If you scan a card at a store that's more than 20 minutes away from your house, "they" know it's safe to break in to plant bugs and stuff. And if you claimed to be a low-carb vegan on your (socialized) medical insurance forms, you got some explaining to do...
OK, yes, I'm being paranoid, and, yes, they can get even better info if you drive (license plate reading cameras) or use a credit card. I'm just bringing attention to the importance of putting a value on privacy. If more people shared this cultural trait, free market competition between stores would find a way to give you a 20c discount on oat cereal without tracking your identity in the process...
As for my alias tracking scripts: what happens on the (public) Internet stays on the Internet... That's the reality of efficient information systems: access to information is easier than what people are used to IRL. This forum is spidered by Google on daily basis, and there are 1000s of other major search engines out there, and bandwidth and storage will only get cheaper... So don't post personal info on a public forum if you don't want that info proliferated indefinitely! Sure, I'm a nice guy, I might remove real names and stuff from my lists upon request (though I can no longer edit the threads created by accounts I've deleted). Good luck getting all the search engines to do the same...