I've been using Enigmail for about a decade, and PGP longer than that, and I still think it's a pain in the ass. Whenever I'm configuring a new mail client, I have to fiddle with multiple settings just to get it to send encrypted mail.

There's a real opportunity to build something much, much simpler on top of PGP. All you really have to do is pick some sensible defaults and automate a few steps. Look at how many nerds can't be bothered with encrypted communication, let alone normal people.