I have an iPhone and and iPad (iOS 6) and a mac (moutain lion). I have problems syncing my calendars between these devices. I think the problem started when I configured my new MBP in 10.8
a) I do no get error messages on iOS devices by the idevices'calendars do not sync with the mac's (even all of the three are set to use the icloud calendar on the same account)
b) on the mac, I get a error message when syncing "could not create event because of a server error" or something similar
c) on the mac, after connecting to icloud.com is safari, I see that my iCloud calendar is almost empty. I try to create an event, and I get a message "cannot create event because of a server error". I tried diconnecting and reconnecting to icloud.com several times, and the same thing happened again and again. I sent the report to Apple each time
Everything worked fine before I stated using iCloud. Syncing through USB was long but it worked. Now this does not work anymore.
To be honest, i would be happy to come back to the snow leopard situation when my computer was still personal.