Email backups are encrypted with your account password, but be careful because if a hacker gains control of your email, or dropbox account, he could use it to spend your coins (if he knows your password), even bypassing 2-factor authentication.

Blockchain.info has a nice feature, which lets you decide a different password required to spend your coins. This is supposed to reduce further the risk of being stolen because your private keys would stay encrypted until you really need them.