In addition to the types of data mentioned in other replies, they also have:
- Mail and calendar for people who use the iCloud services.
- Reminders.
- All documents (e.g. Pages, notes) synced to iCloud.
- Mail and calendar for people who use the iCloud services.
- Reminders.
- All documents (e.g. Pages, notes) synced to iCloud.
Not to mention the fact that a users interaction with Facebook is completely different from their interaction with Apple. Most people keep especially private data off of Facebook, but practically no I-phone user stops to think if a photo might be incriminating/embarrassing in the future before they take it. And that's just Photostream.
People backing up their devices to iCloud stand to lose even more.