October 12, 2011, 2:41 PM — Within Apple's new iCloud service, you can sync, back up your devices, and locate friends--but if you want to manage your music and purchases, look to the service's iTunes in the Cloud initiative: For free, you can automatically download any new purchases across all your devices, and access any past purchases (still available on iTunes); pay an extra $25 a year, and you can store and stream your music online with iTunes Match. Here's how these all work.
Both iOS 5 and iTunes 10.5 include an automatic downloads feature that lets you choose to have your device or computer automatically download any music, books, and/or apps you buy on other iTunes-running computers or iOS devices. (Note that it also works with any free content in those categories that you've downloaded.)
iTunes: To set up automatic downloads in iTunes, go to the Store tab of iTunes's preferences. At the top, you'll see an Automatic Downloads section, in which you can individually enable the downloading of music, apps, and books purchased using your iTunes ID. Click in the box next to each that you want to enable and then click OK.
iOS: On an iOS device, go to Settings -> Store and you'll see the same Music, Apps, and Books options as in iTunes. To the right of each option is a toggle switch that turns downloading on or off for each type of content.
One particularly nice use of the automatic downloads feature comes with regards to books. Starting with iTunes 10.3, Apple has allowed you to browse and purchase (but not read) books from the iBookstore from within iTunes itself. Even on the iPad's large screen, an iOS device isn't the best way to look at the vast selection of books on offer, so if you set up books downloading on your device, you can find and purchase a book from your computer and then have it ready for you to read the next time you launch iBooks on your iPad.
Previously purchased content
Another part of iTunes in the Cloud is the ability to re-download previously purchased content. Previously, this was available in beta for users of iTunes 10.3 and iOS 4; with iCloud's release, it's available for all iTunes 10.5 and iOS 5 users. Apple now lets you re-download any music, books, apps (you could always re-download apps, but it wasn't an obvious process), and TV shows (in the U.S. only) that you've obtained via the iTunes Store, App Store, or iBookstore in the past. (Note that you may not be able to download content that's no longer available from Apple's various stores.)
Apple currently doesn't let you re-download movies, audiobooks, or podcasts.