The department wants the data to try to show in court it has the right approach in enforcing an online pornography law.
I wouldn't call ordering a company to hand over (somewhat) confidential records for basically no reason at all the "right" approach.
F*****s.
I'm not sure what value it would have beyond advocating government censorship, anyways - what could it show beyond that some people access porn on the internet (the shock!)? Unless they plan on using that data to track down the identities, locations, etc of people (which would be a massive breach of privacy for everyone else, as they'd presumably have to data-mine access records for a number of sites etc to try and cross-match). Perhaps they want to follow the Chinese approach and place regulations upon the likes of search engines and ISPs (essentially, the Chinese approach is to force self-censorship upon the likes of those groups, and internet cafe owners, etc through punishment as well as the great firewall- thus meaning the state itself is spared from the task of monitoring millions of sites itself).
And this is from the country that controls the internet.
EDIT; based on this
http://www.washingtonpost.com/wp-dyn/content/article/2006/01/19/AR2006011903331_2.html, they want this basically to prove that people can access porn via search engines (no ****, sherlock); possibly with the intention of proving that having the DoJ watching you is better than filtering software or somesuch. What a stupid excuse for such a massive precedent in harming privacy.
