I use 2 OS X machines and an iPhone (I have an iPad too but I almost never use it). And I've never had iCloud eat anything. The worst behavior I've ever seen is

I use 2 OS X machines and an iPhone (I have an iPad too but I almost never use it). And I've never had iCloud eat anything. The worst behavior I've ever seen is upon rare occasion having iCloud take longer than expected to sync changes made to stuff in iCloud Drive, but that's it. During the OS X betas, I've had some issues with the underlying daemons that manages iCloud sync (e.g. bird), but that was a developer beta so it doesn't really count, and it still never actually lost data.