The data security and data privacy concerns on using cloud services or hosted application (like web email) is holding people. The incident in Paula Broadwell showed law enforcement agents had far move power and means to access individual data than we think of. If you like to understand the legal framework on this, there is a very good paper wrote by three Netherlands legal researcher.
W3C has a working group on Web Cryptography and they is developing a library standard for JS cryptography. Below are some user cases, for how the new Web Cryptography API is designed for