Just adding another voice to this. For me it's important that I can get to most of my notebooks without having to use a password because I use it 'on the hoof' to record all kinds of stuff and don't want to be slowed down tapping in a password on an iPhone etc.
However I would like some notebooks for sensitive information that are password protected. I'm not worried about the CIA or any such concerns that need encryption, I just don't want other people using my computer to be able to see some stuff.
As it is I use the 'Day One' app which is perfect for the security that I require but the text formatting is too limited and I'd ideally use evernote if I could