Well, I had read about this a while back, but a recent Slashdot post brought it to my attention again. Did you know that the US Government convinced printer manufacturers to encode every page of a document with a pattern of yellow dots to identify the printer (and user)? If that doesn’t give you an uneasy feeling about surveillance than I don’t know what will.
Secret Printer ID Codes May Be Illegal In the EU
Is Your Printer Spying On You?