"It just works" is the goal of Apple's new cloud based hosting service. All of your info and media can be synced across all devices, iOS and Mac. That info can include contacts, calendars... and even apps and iBooks! And with Documents in the Cloud, even your work content, like Pages, Numbers and Keynote, can be shared! And developers can integrate the cloud into their apps. Plus PCs can participate, too! PhotoStream does the same for photos. And photos can be viewed instantly on your other iOS devices, iPhoto on your mac or even on an Apple TV! This is like my digital camera with Eye-Fi, an SD card with wifi built in.
Mobile Me, formerly $99 is now replaced by the FREE iCloud service! You also get wireless backup will make it easy to upgrade to a new iOS device. Just enter your iTunes ID and password, and your content is migrated. No wonder it's free... This will make it so easy to stay in the iOS ecosystem!
You can also use the cloud for music. You can access all music previously purchased via iTunes and download it on only iCkoud supported device without paying for it again. You can also choose to keep devices in sync, so a purchase made on one device is automatically downloaded on another, up to ten devices total. Every iOS 5 user gets 5GB of storage for free, and you don't have to worry about your purchased music, books, apps, and photo stream, as that doesn't count towards the limit.
One more thing! What about music you imported into iTunes? ITunes Match will scan your library and if they have the same song, they will authorize your iCloud account to effectively own those songs! This is done in minutes unlike Amazon or Google that require you to upload your music which could take weeks! If Apple doesn't have your songs, you can upload those, up to 20,000 songs and iTunes match costs $24.99 per year.