Apple's iCloud explained

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Introduction to iCloud
First up, we should say that the main purposes of iCloud are to allow you to have all of your content safely backed-up in the cloud, as well as to have it seamlessly synced across your iDevices. But even if you only have an iPhone, for example, and no other Apple device, iCloud is still a very cool service, as it will help you restore all of your information and content to you new iPhone, should you decide to upgrade. You just get your new handset, log in with your Apple account, and that's it, as if you've never left your old device.
The basic, free iCloud account comes with 5GB of cloud storage. This storage is used for the content that you create on your device (images, video, documents, etc.), as well as the data that your apps generate (purchased books, in-app downloads, etc.). But this cloud storage is not used to store your apps or music, for example. Since all apps and music are already available on Apple's servers, iCloud simply remembers what apps and music you have, and that's all. It doesn't duplicate the content by copying it to your account as well. Of course, should those 5GB turn out insufficient for you, you can always add 10GB more for $20 a year, 20GB for $40 a year, or 50GB for $100 a year.
How iCloud works
Taking over control of the MobileMe services, iCloud now offers back-up of your Contacts and Calendars. It also allows you to create an “@me.com” email account, which can also sync your notes. The other basic stuff that iCloud backs up are your reminders (created in the Reminders app), and your Safari bookmarks.
Things can get a bit more confusing when it comes to backing your photos and video up. This is largely because Apple has also developed the Photo Stream service, which is an additional way of keeping your photos in the cloud. The thing is that the photos and video you've taken with the iPhone's camera are being backed-up to the cloud by default. Naturally, this counts against your cloud storage. If you want, you can turn Camera Roll backup off, which will free up some space on your iCloud, but of course, your images and video will remain stored locally, on your iPhone. This is where Photo Stream comes in. The service actually lets you have your photos (sorry, no video) backed-up in the cloud, without this taking from your precious cloud storage. However, there are some limitations to Photo Stream that should be considered. First of all, Photo Stream only keeps each photo that's been uploaded (upload happens automatically) for 30 days. After that, your photo is removed from Apple's servers. The other limitation is that you can have up to 1000 photos in Photo Stream. Should you exceed that limit, the oldest ones start to disappear. The way to actually save your photos from disappearing is to manually move them to an album on your device. This will safely place them on your local storage. On one hand, these rules may seem annoying, but on the other, we shouldn't forget that this is just an additional treat for customers, allowing them to have their photos in the cloud, albeit for a limited time, without this taking any cloud storage.
Overall, document management is also greatly simplified with to iCloud. For example, if you're working on a Pages doc on your iPhone, and you're done for the moment, but plan to continue later on your iPad, you basically won't have to do anything, because the doc will automatically sync with iCloud, and from then – with your iPad. Right now, apps from the iWork suite support this functionality, but third-party programs should be able to add support soon as well.
Thankfully, you have the option to disable back-up for each app separately, so that you can choose to sync only what you wish. And that is pretty much all there is to iCloud. We believe it's a pretty useful service that can greatly simplify the user experience with our Apple devices. It's not perfect, of course, it has its own limitations and peculiarities, but on the whole, it's one very polished and streamlined offering. What are your thoughts on iCloud? Are you looking forward to taking advantage of it, or rather, don't find much sense in it? Feel free to sound off in the comments below!