It sounds bizarre, but did you know that your color printer has likely been modified to provide information about your use of it to law enforcement? Yes, I know. I couldn't believe it either.
In many color printers, there are tiny almost-invisible hidden yellow dots generated on each page which can be decoded to reveal the serial number of the printer used and the date and time of printing. Apparently this practice was first brought to public attention in this article in PC World about a year ago. Then the Electronic Frontier Foundation started investigating and produced this white paper. This month the EFF announced they have decoded the dots and published this Web feature "Is Your Printer Spying on You?" with links to many resources including a chart of which printers do and which printers don't. The Washington Post ran this story on the topic yesterday. (WashingtonPost.com may require free registration.) The rationale for this practice was the Secret Service could use it to track counterfeiting. One researcher said he found the "feature" in documents produced by ten year old printers. (Thanks to Norman, OK attorney Kevin H. Pate for bringing this to my attention.)