Missing calendars after upgrading iOS4

I noticed that some of my calendars was missing after I loaded the new iOS4 into my iPhone 3GS. What I did to recover it was:

1. Go to [Settings]
2. Select [Mail, Contacts, Calendars]
3. Select the Account(s) that has missing calendars
4. Turn OFF the calendars
5. Press the [Delete from My iPhone] button
6. Turn ON the calendars again

Turning your calendars OFF and ON again will help to refresh your missing iPhone calendar! Wait for awhile after that for your events to be populated again... I waited for 3-4 hours!!!

However, after looking at this thread from Google support forum, it may be due to Google's mobile server being overloaded with many people trying to sync their Google accounts in such a short period of time after the iOS4 upgrade.

So which is which? Apple's iOS4 or Google's server problem?