iCloud synchronization to push data caps to the limit
Keeping so much data synchronized in the background as described by the iCloud announcement is a useful service, but it moves so much data that it may be pushing capped mobile data plans into the red zone.
One of the most useful features announced by Apple today at the WWDC keynote is the iCloud service that is aimed at keeping user data in sync across multiple devices. This data synchronization is not limited to documents; as described by Apple, it covers apps, music, photos and just about everything. Keeping so much data synchronized in the background is a useful service, but it moves so much data around that it may be pushing user's capped mobile data plans into the red zone.
The synchronization as described by Apple is very prolific, and will make Mac users who own iPhones and iPads (and that's a lot of you) able to access all of this content no matter which device you may be using. Such access is a nice thing, but it requires the constant movement of data around the user's personal cloud. This has the potential to eat up the mobile data caps in place on iPhones and 3G iPads.
Every time a document is created on one of these devices, it is shot to all the other devices owned in the background. One document is pushed to two devices for those who use a Mac, iPhone and an iPad. It isn't just moved around once, with the new Revisions in OS X Apple is keeping full versions of each documents, and it sounds like those will be pushed around to the other devices too.
That is just document creation; when you buy a song (or album) on iTunes on one of these devices, it's getting pushed to the other two. Add in backups and document synchronization and the possibility is very real to have data flying around a lot of the time. This will all be subject to these data caps imposed by the carriers, so iCloud users may start finding themselves in overage territory.
Apple may be covering our backs and make such synchronization configurable to only happen over Wi-Fi, but that has a toll too in my experience. I have used either Dropbox or SugarSync to keep multiple devices in sync like this, and when I did it only on Wi-Fi it hampered the overall benefits. Since syncing wasn't happening all the time, I couldn't assume the file I accessed on one device was in fact the latest version on another. The mindset gets adjusted to having files always in sync, and when circumstances (like being away from Wi-Fi) prevent that from happening it creates problems. Add in the extra time that is required when iCloud could resume syncing, due to playing catch-up, and it quickly becomes a pain when Wi-Fi is finally available.
The iCloud service sounds wonderful, and I am pretty sure I will be giving it a try when it's available in both OS X and iOS 5. I do think it's worth keeping an eye on mobile data usage once it gets rolling.