Apple’s free iCloud service—formerly MobileMe, formerly .Mac, formerly iTools—offers a long list of very useful features. You don’t have to sign up, but you owe it to yourself to know what’s available.

So what is iCloud? Mainly, it’s these things:

  • A synchronizing service. It keeps your calendar, address book, and documents updated and identical on all your gadgets: Mac, PC, iPhone, iPad, iPod Touch.

  • An online locker. Anything you buy from Apple—music, TV shows, ebooks, and apps—is stored online, for easy access at any time. For example, whenever you buy a song or a TV show from the online iTunes store, it appears automatically on all your i-gadgets and computers. Your photos are stored online, too.

  • Back to My Mac. This option lets you grab files from one of your other Macs across the Internet. See Variations on Screen Sharing.

  • Find My iPhone—and Mac. Find My iPhone pinpoints the current location of your iPhone or iPad on a map. In other words, it’s great for helping you find your i-gadget if it’s been stolen or lost.

    You can also make your lost gadget start making a loud pinging sound for a couple of minutes by remote control—even if it was set to Vibrate mode. That’s brilliantly effective when your phone has slipped under the couch cushions. In dire situations, you can even erase the phone by remote control, preventing sensitive information from falling into the wrong hands.

    In iCloud, this feature can find your Mac, too. That might seem like a silly idea; how often do you misplace ...

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