Most of iCloud's services use CRDTs underneath I believe. That includes Notes, Reminders and possibly Photos as well. FoundationDB is some of the backend as well. I was told this by a drunken former Apple SRE in a bar :)
The other day I saw a bug in it, when editing a Note that another person was also editing. We were editing separate paragraphs. My cursor kept resetting to the beginning of a word after each letter I typed (and the Swype-style keyboard had the same problem). My point is, even Apple Notes doesn't get it quite right.
