Earlier quoted context omitted.
You don't have to guess -- they specify exactly what is encrypted in iCloud; "On devices running iOS 8, your personal data such as photos, messages (including attachments), email, contacts, call history, iTunes content, notes, and reminders is placed under the protection of your passcode."
But "iCloud does not encrypt data stored on IMAP mail servers" or Notes http://support.apple.com/kb/HT4865
Well, no shit. If they did that I'd log into my Gmail web interface and see encrypted gobbledygook instead of my emails.