Apple’s iOS 8 update will be released tomorrow (as I write this) and if history is any indication, millions of iPhone, iPad and iPod touch users will hit that update button en masse.
I think that’s fine; the “Gold Master” (GM) version of iOS 8 seems very stable, and while many of the update’s best features won’t really come into play until the release of iOS’s desktop cousin Yosemite, it’s got enough nice new features to make it worth using.
But it’s that very partnership with Yosemite that makes it an extremely good idea not to upgrade your iOS device to iCloud Drive when prompted. That’s because iCloud Drive isn’t compatible with Mavericks, Apple’s current desktop operating system. Nor is it yet compatible with current versions of the many apps that use iCloud (sans the “Drive”) to do things like store information, sync data and do various other things that you are very likely to miss when they suddenly stop working.
Our friends over at TidBITs have more information, but for the time being suffice it to say you should just hold off on iCloud Drive until Yosemite is released and app developers release iCloud-compatible versions of their wares.