Again, if you're not typing the password in every time, a local compromise is almost certainly game-over. Apple's keychain helps reduce the damage if the data's not actively used but for something like CrashPlan which is always running the attacker is probably going to be lucky.
However, you can also secure the encryption with a password not associated with the account. Or even provide your own 448-bit key. If you do either of these options, CrashPlan support will not be able to help you
This setup allows CrashPlan to easily help non-technical home users, while allowing technically savvy users to securely hang themselves with their own encryption.
Furthermore, you can use the encryption key + a custom password, or your own encryption key with a passphrase. In this case, it is encyrpted locally and the key is not sent to Crashplan[1].
[1] http://support.crashplan.com/doku.php/recipe/change_security...