http://seeingyellow.com/ (It would be nice if anyone could confirm this, since I don't own a color laser printer to check for it myself)
I doubt that you could track an individual this way. The retailer would need to record the serial number of the printer and link it to an account on the retailer's systems [which would hold your name/address/phone]. This is presuming that, if the story is true, then there are unique patterns that correspond with specific serial numbers. This isn't workable since color laser printers can be procured from anywhere, without any form of identification, since they're not a restricted product of any kind. Can law enforcement agencies match various of types of patterns on printed media to the printer you own? Sure. They would have to already suspect you of the crime, though, and would simply be comparing the document to your printer to confirm you produced it. There's no covert surveillance here. They can't take a document you printed anonymously and then deduce who you are from that. I think the part of the story about "Secret Service agents" showing up the subject's door is also far-fetched. It is doubtful that any "secret agency" is going to waste time sending field agents out just because someone asked about these apparent patterns. If anything, the only possibility for actual "tracking" would be to ship printers with specific patterns to specific regions. This way you could narrow down where your target purchased the printer and possibly increase the chances of locating them. In reality, this pattern technique would mostly be useful for linking printed documents to a known subject who is already under surveillance. A printed document could only be traced to a particular location if that printer were registered to an individual or business [either voluntarily or by the retailer linking the serial number to their customer record].
I'll have to look this up, but there actually is a real method to this and it can be used to track you. I believe this particular article is overstating it a bit, but there actually is tech built in to them to do this. Edit: Have a look here for now: http://www.eff.org/issues/printers , and here: http://w2.eff.org/Privacy/printers/docucolor/. Other Google searches come up with dated articles from the Washington Post, PCWorld, and others. So, this isn't a fantasy.