What is iCloud Drive?
After upgrading iOS 8, I was prompted to "Upgrade to iCloud Drive." What should I do?
You can upgrade to iCloud Drive if all your devices are running Mac OS X 10.10 Yosemite and iOS 8. If you need to sync with devices that will continue to run earlier versions of iOS and Mac OS X, do not upgrade to iCloud Drive. (Grid Diary 3.2.0 requires iCloud Drive.)
If I don't upgrade to iCloud Drive now, can I do so in the future?
Yes. You can upgrade to iCloud Drive later.
I updated to iCloud Drive, and I want to revert to iCloud. Can I do that?
Unfortunately not. Apple does not allow people to revert to iCloud after they have made the transition to iCloud Drive.
Is there an alternative to iCloud so I can sync my diaries across all my iOS devices?
Yes. Started from 3.2.0, Grid Diary supports Dropbox and WebDAV for syncing. For more details about other sync services and Grid Diary, see: Syncing with Dropbox, Syncing with WebDAV.