Until 2012, Apple sold a $100/yr package called MobileMe. It gave youa mail address at "me.com", the ability to publish web pages and a photo gallery online, file storage, a "Back to my Mac" service, and the ability to share contacts, bookmarks, and calendars with iPhones for about $9/mo. Another feature of MobileMe was that you could locate your iPhone, useful if it gets lost or stolen.

iCloud

MobileMe has now been superseded by iCloud. Apple says it "stores your music, photos, documents, and more and wirelessly pushes them to all your devices." Up to 5GB of storage is free with a new Apple device; you can buy more capacity: $100/yr gets you 50GB of iCloud storage.

What is still there

iCloud provides each user a mail address at "mac.com". (If you have a "me.com" address, you can keep it.) "Find my iPhone" works for Macs, iPads, and iPhones. "Back to My Mac" works between Macs running Lion, providing remote access and screen sharing.

What's new

iCloud is integrated with iTunes and allows you to keep your music and purchased books in the cloud, and use them on any of your Apple devices. iCloud is also integrated with iPhoto, and lets you store your "Photo Stream" in the cloud. These services don't count against your storage quota. Documents written by Apple's iWork applications can also be synced to iCloud (sort of like Dropbox, but only for Apple). There is an iOS 5 app, "Find my Friends," that lets family and friends using iPhones, iPads, and iPods find each other, up to 50 friends.

What goes away

MobileMe's ability to publish web pages, its online photo gallery, and iDisk storage are gone: you can find similar free services from other companies. iCloud does not support syncing of Mac Dashboard widgets, keychains, Dock items, and System Preferences from your Mac.

What else you need

You still need a home dialup or broadband ISP, and that may include some services like storage and mail: for example, Comcast provides these. iCloud does not eliminate the need to back up your computer's hard drive: you should still use Time Machine.