Email Encryption

I am doing a paper on email encryption and I have two theories: The level of encryption depends on the information being encrypted. Much email is non-sensitive info so encryption is not used. At other times, like for medical records, email is encrypted to protect confidential info. Email encryption is not used because users don't know how much it is worth. Email encryption developers need funds to create privacy, but different users value privacy differently. Many users want free online privacy, expecting it to be "provided" by the Net. Others, like corportate users, will pay resonable fees to companies (like Verisign) because they need strong encryption. What I need are papers, books, or other documents that back up (or refute) the above claims. If anyone has user survey data (how users value email encryption) that would be ideal!