Mike Outmesguine of Wi-Fi Toys learned that his color laser printer prints out those traceable forensic dots (which indicate the time, date, and serial number of the printer — here's EFF's list of Orwellian printers) on the back of the pages, which makes the printing process much slower.
You see, I have a duplex color laser printer (HP 4600dn) which can print on both sides of the paper. One of the annoying things I discovered early on with this printer is how it prints single-sided jobs: it actually prints out (what I once believed was) a blank sheet, then sucks it back in the feeder and prints the content on the back of the page. (If you are doing letterhead, you have to put the paper in upside down.) That is annoying in itself.
However, I compared the forensic dots on both sides of a single-sided printed sheet with a blank sheet from the feed tray. The printed sheet has dots on front AND back. The printed side, and the non-printed side have the dots while the blank sheet is just that: blank.
