Resource: Nik Fletcher — iOS 8 & iCloud Drive

Nik Fletcher (Realmac Software) —

If you upgrade to iCloud Drive, you will only be able to sync with devices running iOS 8 or OS X Yosemite. As OS X Yosemite is still pre-release (and not yet available) upgrading to iCloud Drive will prevent you from syncing with Clear for Mac until both OS X Yosemite is released and you upgrade to OS X Yosemite.

Developers cannot work around the choice made when upgrading to iOS 8, so please make sure you pay close attention to the iCloud Drive screen shown after you update to iOS 8.

This is going to be a problem.