Here's something useful from iOS 5! Following the devastating earthquake and following tsunami on March 11 of this year in Japan, Apple has added a new early earthquake warning notification option in their upcoming iOS 5. Japan-based iOS 5 users can turn on early earthquake notifications at the very bottom of the iOS 5 Notification Center settings pane. All that is required is the flick a switch (as shown below in the picture) and if an earthquake hits, you'll get anything from a few seconds to one or two minutes warning before the earthquake hits.
Time profiled Japan's earthquake warning system this year and explains the history of the system:
Japan has the most advanced earthquake early-warning system in the world. A nationwide online system launched in 2007, it detects tremors, calculates an earthquake's epicenter and sends out brief warnings from its 1,000-plus seismographs scattered throughout the country, one of the most earthquake-prone nations on the planet.
For those of us who can't read Japanese, the picture above also says that the feature may reduce your battery life as it is always connected to Japan's earthquake warning system.