Andy Greenberg at Forbes has shown us the information that law enforcement can recover via a seized iPhone. The article is essentially in response to one published by the American Civil Liberties Union highlighting the amount of information the US Immigration and Customs Enforcement (ICE) agency was able to gather from a suspect's iPhone in the course of a drug-related investigation, using forensic analysis with the help of a specialist company.
Perhaps the most surprising thing about this is that so many people seem to find it surprising, even though police procedural dramas often ascribe even more arbitrary powers of data recovery (with or without a warrant) to investigators. You might or might not share the ACLU's concerns about the ease with which real-life investigators are able to conduct such searches, and I'm not going to get into the 'it doesn't matter to people who have nothing to hide' debate, either.
But it's worth remembering that you don't necessarily need expensive forensic programs and hardware to get quite a lot of information from a smartphone – almost irrespective of the operating system and manufacturer. It’s especially true if you don't take elementary precautions like restricting access with PINs and passcodes – or other authentication systems.