I have used MobileMe for many years with no issue syncing between multiple computers and devices. However, Apple released a new version of iCal and when I upgraded I not only lost a lot of data, but it cancelled a bunch of appointments and emailed my contacts automatically telling them I had cancelled our meeting. This happened twice and I spent a lot of time on the phone with apple tech and none of them could tell me why this happened.

However, having said that, I never had any problems until this past year when apple did a significant update to the way iCal works and syncs withIn MobileMe.

I always do regular backups in all my programs so I was able to restore my data.

I moved off of iCal to BusyCal for Mac, which is a much more robust calendar program for the Mac. It works better for me. But I still use iCal on the iPad and iPhone. Busy Cal syncs fine with iCal, but manages the data and invites better on my desktop.

I suggest installing Dropbox on all your devices and doing backups that way. I auto backup omnifocus to Dropbox.