I upgraded my iPhone first, on the first day of the official IOS5 release. It went swimmingly. I only had to restart the upgrade 5 times to get through and I was done. I switched to syncing with iCloud, syncing some content with my macbook air via wifi; I was really using the features, I felt.
Then, I upgraded my wife's iPhone to IOS5:
- Started with a sync for a backup
- I did the upgrade (which also takes a backup - a full one this time I believe)
- I set it to back up to iCloud (and promptly forgot I did this)
- Synced with my laptop for a backup (which it was not because of the iCloud setting)
- set for iCloud sync
- merged all of my 8 gazillion contacts and hugely numerous calendar items with my own
- Turned off iCloud sync
- Deleted all contacts and calendar entries
- A recovery to the last known backup (related to the upgrade I thought but seemingly no) - still no calendar or contact entries.
- Resync all contacts and deleted all of my contacts (various times for hours during one day)
- Manually copied calendar entries from mine (hours during the next day)
You cannot sync the iCloud Photo Stream to and from multiple iPhones and have a separate calendar also synced to iCloud from those phones. Point learned.
So in the end we chose separate iCloud accounts and no Photo Stream sharing to each other.