Lacey and Larkin, who have long battled with Maricopa County Sheriff Joe Arpaio and County Attorney Andrew Thomas, wrote a story about the subpoena because they considered it an attack on the freedom of the press. The subpoena demanded records relating to all visitors to the New Times website over the last four years, including information about what websites they visited prior to the New Times website (i.e., referral URLs)--essentially, the request is for the complete website logs for the newspaper's website for the last three years. It also demanded reporters' notes and any other documents pertaining to stories about Arpaio for the last three years.
Lacey and Larkin wrote that they believed their article to violate the law, but they published it as a form of civil disobedience in order to challenge the unconstitutional abuses of Arpaio, Thomas, and prosecutor Dennis Wilenchik.
The trigger for the events which led to the subpoena (and the apparent event of interest given the dates in the subpoena) appears to be a New Times article from July 8, 2004 which commented on Arpaio's commercial real estate investments and ended with Arpaio's home address, but the paper's criticism of Arpaio for mismanagement, inmate deaths, and grandstanding in front of TV cameras goes back many years more.
Sheriff Joe used to have a dialup Internet account with Primenet, my former employer. At one point one of his assistants, Lisa Allen, contacted Primenet to attempt to get information about a subscriber who had left a critical comment on his website, without a subpoena. We declined to provide such information without a subpoena.
UPDATE (October 19, 2007): County Attorney Andrew Thomas has announced that he has dropped the charges against New Times and dismissed special prosecutor Dennis Wilenchik.
UPDATE (November 13, 2007): New Times ran an October 25 followup story.
UPDATE (October 28, 2008): It has come out that the order for Lacey and Larkin's arrest was given by Arpaio's chief deputy David Hendershott, whom Arpaio allowed to retire so he could receive a $43,000/year pension, and hired him back as a civilian at his same $120,000/year salary. Hendershott now makes $177,486/year working for Arpaio.