interesting information via the EFF:
Given that much of Mr. Harris Twitter information like Tweets and followers is already public, its very likely that the government was really after something else: location data. By attempting to subpoena these records, the government can get around the Fourth Amendments prohibition against warrantless searches by requesting information that includes IP addresses. Twitter keeps track of IP address information regarding every time a person logged into Twitter, as well as the IP address information related to a Twitter users direct messages to other users, and the date and time information related to these log ins and direct messages. Armed with IP addresses, the government — without a warrant — can go to an ISP to determine who was assigned that particular IP address. And if that person connected on a mobile device — which is where the majority of Twitter users access their accounts — the ISP will hand over to the government the specific cell tower and its corresponding geographic location which that person used to access Twitter. This allows the government to piece together a map of where a person physically is when he opens Twitter on his smartphone, sends a direct message to a friend, or Tweets. And with that information, the government could get a record of Mr. Harris movement over the three months it requested from Twitter. Its no surprise then that the government singled out Mr. Harris for this request: he currently has over 1,500 followers and 7,200 Tweets.