This article describes how the LAPD online crime map mistakenly geocoded 1,380 crimes to a spot directly in front of the LA Times Office because it was the default location for unmatched geocodes. This mistake then lead to the popular site EveryBlock to rank that ZIP code as one of the most dangerous in the city. Lesson learned: don't believe every dot on a map is the absolute truth.
Another interesting article describes how analysis of an FBI database links long-haul truckers to serial killings. This shows that local data linked together can change the scale of analysis to reveal a "mobile crime scene".