The best way to push the adoption of GPG is through a HTML5 crypto API that would include it. A social network or email service that doesn't work in the browser would be inaccessible from cyber-cafés or from work (two of the most popular accesses to the web in developing countries).
I usually try to avoid sweeping generalisations, but in this case... I just can't see any use at all for crypto communication where the end-points are not secure.
