Dan Moren has a nice writeup of a recent experience where iCloud services were unavailable to him and how Apple’s black box approach makes understanding why an impossible task.
I use iCloud services regularly and have noticed occasional sync issues (less common now than in the past). Troubleshooting is difficult because you have no way to attempt a manual sync or view a status message explaining that, yes, you are having a problem.
It is just something to remember because no matter which service you use to store your data you don’t have full control, things may go wrong, and you might not always be privileged to know why.