While we're cataloging security technologies that have failed, we should add S/MIME-based email encryption to the heap. (Well, except for those organizations that have centrally-managed keys and infrastructure for internal email encryption.)
I know that some savvy users encrypt email, but in the age of the NSA, payload-encrypted email should be the default case.
We should thank MUA and browser vendors for that - they made everything to keep UIs as scary and unusable as possible.
It could've been different if MUAs had allowed (or even suggested) users to generate keypairs and send CSRs in a simple streamlined way. Maybe even cooperate with StartSSL and alikes (like Thunderbird cooperates with file hosting services to send large attachments, huh) to automate the request sending and validation.
As another recently posted article points out, missing $180 billion per year in foregone revenue isn't motivation enough to get US tech companies to make verifiable clients, easy s/mime, key exchange and web-of-trust features of their systems. How big a clue-stick do they need?
I suspect it will only catch on once the big email providers find a way to make it transparent and cost-effective. And we start seeing verification icons in email clients above our messages. That way humans know it matters ;-)
The thing is, you can do that today with Apple's Mail.app, and have been able to do so for years. I sign my email using S/MIME, and while that wound up causing problems with a few outdated mail clients 5 or 10 years ago (sometimes, the fact that it was signed would make certain clients with poor MIME support show the body of the email as an attachment, which confused people), it doesn't cause much problem these days.
Cool. Still not as convenient as it could be, though. "If the intended recipient is outside the sender's Exchange environment or if the sender is not using an Exchange account, the recipient's certificate must be installed on the device."
What that means is by default any email you send would never appear "trusted" so... It's not a great marketing device. A green address bar does more to market SSL than its own advantages, sometimes. I'd argue that certificate trust -- even to say that the email address belongs to gmail.com, for instance, would do wonders to promote the technology.
Sadly, no support on Android, since apparently on Gmail everyone only emails within Google services and never for businesses? ;-) Microsoft should promote SMIME in its online Exchange offerings more, to compete with Gmail.
I know that some savvy users encrypt email, but in the age of the NSA, payload-encrypted email should be the default case.