The one glitch I have had here is that the upgrade process may take an unusually long time, with the spinning wheel seeming as if it will never stop. Be patient. However, if you eventually believe something has gone wrong, you can log out of MobileMe and log back in. When I did this, I found that the upgrade had successfully completed; the new Calendar happily appeared. Otherwise, you can select to upgrade again.

4. Assuming you've already been syncing your calendars via MobileMe, when you next launch iCal on your Mac, iCal should automatically update your calendars to reflect the change. In particular, your calendars will now be listed under a "yourname@me.com" heading. If not, check out this or this for advice.

5. Go to System Preferences and open the MobileMe pane. From the Sync tab, uncheck the Calendar option. As you are no longer syncing calendars via Sync Services on the Mac, this option is no longer needed.

6. If you also sync your calendars to iOS devices, go to the Calendar app on each device. If all has gone well, the app should automatically reflect the new calendar service. If you see the same calendar(s) listed more than once, or otherwise have problems, check out the same two Apple articles cited above. For me, the key remedy has been to go to the MobileMe account settings in Settings -> Mail, Contacts, Calendars; tap the Calendar slider off; and choose to delete data when asked (this assumes your data remain at me.com). When you turn the slider back on, calendars should now display correctly.

7. Finally, if you use BusyCal, you'll have some additional work to do. In fact, don't even begin the transition until your read this .