Lately, I've noticed that iCal is deleting events when I sync with iCloud.
The problem occurs because I don't have access to the internet when I travel about during the day, I might create some reminders for myself so I don't forget to do something, then I come home, connect my Macbook Pro to the internet (WiFi) where iCal proceeds to sync. Then, all the events I've added whilst offline disappear. Sometimes, they reappear a few hours later, but are basically unmodified from when I create them (they have a name and date applied, but no "custom" options).
Because of this issue, I've lost important information that I REALLY NEED to have on hand when I get back home sometimes (I include extra info in the Notes section of the Events customization dialogue).