Running 10.8.2, and the alerts that I set up for my Birthday events repeatedly disappear. This is the automatic Birthday calendar, where it pulls the dates from Contacts. I'll painstakingly set up email alerts to remind myself a week prior to someone's birthday. Then a couple days later I'll notice I'm not getting the alerts, I'll check Calendar, and the alerts have disappeared.
I've tried searching, but it doesn't appear that this is too big an issue, because I can't find too many people talking about it.
Is this something going on with Calendar? I have a sneaking suspicion that iCloud is behind this somehow, but I don't have any evidence.
I wouldn't have thought the Birthday events coming from the Apple Contacts app would have anything to do with my Google Calendar that I access through iCal - but the behavior is the same. If I set alerts on the Birthday event, they immediately disappear.