I haven't played with iCloud, but Couchbase Lite + CouchDB on the backend has been pretty great to work with. Data sync is free and Just Works™, and thanks to

I haven't played with iCloud, but Couchbase Lite + CouchDB on the backend has been pretty great to work with. Data sync is free and Just Works™, and thanks to Couch attachments, supports files as well. Not right for every use-case, obviously, but for keeping data in sync across devices it's been great.