I have just turned off icloud & icloud calendar syncing with my Windows 7 Outlook 2010 calendar & contacts on my desktop PC & two iphones (iphone 4 & iphone 5), and won't be using this unreliable service for quite some time until it becomes reliable. Basically I use Outlook 2010 calendar on my PC for my airport transfer business and have been syncing two iphones (using cables) to the PC Outlook calendar. I then decided to set up icloud to sync my Outlook calendar with the icloud calendar etc, so any changes I made in the PC calendar would also get changed on the two iphones & vice versa etc, which is how it is supposed to work. All worked fine for a day or two. But wait!! to my horror & amazement, after a couple of days, I noticed some Outlook calendar transfer appointments had disapeared from my PC & two iphones. I re-entered them again from my paper hard copy & double checked all my appointments again to see if any more had disappeared. The appointments went in OK on my PC & got synced with the iphones using icloud etc. A couple of days later the same thing happened again. Some transfer appointments had disappeared. Its a good job I check & remember, as my customers would be waiting for me to take them to the airport.
A long story short, after speaking to Apple support & explaining this unbelievable problem, I (& them) put it down to icloud outages. What I think is happening (not confirmed by Apple support) is that if I enter transfer appointments into my Outlook calendar, when unbeknown to me there is an icloud outage, then the apointments DON'T get up-loaded to the icloud calander. Consequently when icloud comes back on line, I think that the icloud calendar then syncs back with the Outlook calendar and removes the new appointments I just entered into Outlook on my PC. Which possibly explains why they disappear from my Outlook calendar. I now use the cables to sync my iphones with my desktop PC & Outlook calendar. All works perfectly. I can now also cut & paste again with my appointments, as icloud didn't allow this function.
I hope this message helps people in a similar situation to me, to understand why Outlook appointments disappear. PS, I never did get a return phone call (like promised) from Apple support on a possible explanation or solution to my problem.