This sounds like a great project for a YC startup: make email secure for everyone, and make it as easy to use as DropBox. It sounds mundane, by I think the comments so far are accurate; no one uses GPG, etc., because it's too difficult for non-techies to use. I've tried using several things over the years (even HushMail), but since my colleagues and friends wouldn't, I ended up giving up. I wish I had the chops to create such a thing (I'm a web designer, so wrong side of the brain). I'm sure there's someone reading Hacker News who could solve the problem.