Robert Heaton figured out what most of us figured out was going on anyway.
HP wants its printer to collect all kinds of data that a reasonable person would never expect it to. This includes metadata about your devices, as well as information about all the documents that you print, including timestamps, number of pages, and the application doing the printing (HP state that they do stop short of looking at the contents of your documents).
Scan a document, print it, and HP gets a look at the document, too? Scary.