If they could integrate it in a way where you press a button and it automatically builds certs (on your local machine), and then uses the certs whenever you send the to someone else who had support, then it would be used all of the time.
Usability factors are a huge issue with PGP that have, more than anything else, kept people from using it widely. We use HTTPS all of the time, because it works automatically. PGP has always required a bearded hacker to set up properly and almost nobody uses it.
