I'm pretty sure that this has been happening at least as early as Mountain Lion. I felt really violated when I discovered it - I use TextEdit as a scratchpad, so it's always full of random notes (and a temporary copy-paste spot for private keys, double-plus-ungood!). Not to mention financial data into Numbers - those were being synced automatically, too.
Another gotcha I noticed around the same time - Notes from iPhone are automatically stored to the primary email account. So I had my private scratchpad phone notes stored on my corp account's Notes folder with no easy and obvious way to re-associate them to the correct account.
It's easy to disable, but as the writer notes, that's not the point - if you don't know it's happening, there's not much you can do, just feel your stomach drop, disable it, then get to work figuring out how much damage was caused (i.e., get to swapping keys, ugh...).
Another gotcha I noticed around the same time - Notes from iPhone are automatically stored to the primary email account. So I had my private scratchpad phone notes stored on my corp account's Notes folder with no easy and obvious way to re-associate them to the correct account.
It's easy to disable, but as the writer notes, that's not the point - if you don't know it's happening, there's not much you can do, just feel your stomach drop, disable it, then get to work figuring out how much damage was caused (i.e., get to swapping keys, ugh...).