Once upon a time, a guy named Rob got his iPhone 3G stolen at the dry cleaners. Thankfully, he was subscribed to MobileMe, which at the end saved the day. Or so he says.
According to Rob, after getting his iPhone stolen he went to the Apple Store to buy a new one. He proceeded to set up it up with MobileMe, the service that allows mails, contacts, and all kinds of data to be synchronised with Apple's servers. The synchronised data is then merged into a database, and then pushed to all the devices set with the same MobileMe account.
This was the key to the case. A day later he noticed something weird in his new iPhone: There were contacts which never were there. He quickly realised what was happening: The dumb thief forgot to wipe out the mobile phone, so Rob had the power to identify those contacts—after that, he called them, got the thieve contact information, and told the police, who apprehend the thief and recovered the iPhone.