It's certainly an option, but you must use a client like Thunderbird to do it, loosing the ubiquity of the web interface. Maybe when window.crypto will be standardized and with a good browser extension we will have security and easy of use.

>good browser extension

http://www.mailvelope.com/

https://github.com/crised/SafeGmail

No good (edit: stable and drop-in) Firefox tool yet.

Or just attach pgp files to your e-mail and use it with any e-mail client or server.