Why are my events disappearing in iCal after upgrading to Lion and how can I fix it? I have several calendars synced using MobileMe and after upgrading to Lion it is often the case that a day's worth of newly added events all disappear. This generally happens when I am in another application. Often, if I re-add the same event later, the old events re-appear, giving me duplicates.  However, if I never re-add the events, the old ones never come back.  

The events that are missing from my Mac still appear on my iPhone, but attempting to re-sync does not bring the events back to my Mac.

I have tried clearing my iCal cache and preferences while the events are missing, but this does not seem to bring them back.

So, why are my events disappearing in iCal and how can I fix it?
iOS 5 and iCloud should be coming out tomorrow.  There should be improvements in this area.  Hopefully this will help you.  I know it is not what you would want to hear, but I have seen disappearing content like you describe.  Especially with Exchange, and OS 10.6.x