iCloud is the new Apple service that will ultimately replace MobileMe. If you’re a current MobileMe user, you will get all sorts of “reminders” and nudges to migrate to iCloud or start an iCloud account.

Unless you’re running Lion (Mac OS X 10.7) on all of your Macs, don’t do it.

The problem with iCloud is that it requires the latest OS and won’t work with any previous OS for synchronization of data. If you migrate to it and still have a previous-OS Mac, you will lose the ability to share your contacts and calendars among your Macs and iOS devices, and there is no way back.

The alternative is to start a brand-new, free account with iCloud for a specific purpose on your iOS devices (like backing up to iCloud instead of your Mac), but when you do finally migrate, you will have multiple iCloud accounts and, at this time, there is no way to merge them.

The bottom line is, if you use MobileMe and haven’t completely upgraded to Lion, you don’t have to do anything until June 2012 so leave iCloud alone. But if you don’t have a MobileMe account, or have upgraded all of your Macs to Lion, go ahead with iCloud.

[Written by Kem Tekinay]