My smartphone, the spy: protecting privacy in a mobile age | Ars Technica
http://arstechnica.com/business/2012/03/my-smartphone-the-spy-protecting-privacy-in-a-mobile-age
Under a legal principle called the third-party doctrine, this data does not enjoy the same robust Fourth Amendment protections available to data physically controlled by a user. That means that the government may be able to obtain access to your private Facebook posts and even the contents of your Dropbox folder without getting a warrant.