This is a very old technique. I came across it six or so years ago: the article where I found the code, http://odetocode.com/humor/68.aspx, is from 2003.
It's a lot of fun though. And PJL can be very interesting to work with: I built a tool that used it to query printers for status information (although the amount of information I could extract seemed very dependent on the printer).
It's a lot of fun though. And PJL can be very interesting to work with: I built a tool that used it to query printers for status information (although the amount of information I could extract seemed very dependent on the printer).