Facebook just added optional PGP support for all their email notifications to users:
To enhance the privacy of this email content, today we are gradually rolling out an experimental new feature that enables people to add OpenPGP public keys to their profile; these keys can be used to “end-to-end” encrypt notification emails sent from Facebook to your preferred email accounts. People may also choose to share OpenPGP keys from their profile, with or without enabling encrypted notifications.Source: Securing Email Communications from Facebook
Serious kudos to Facebook for building PGP into their infrastructure. The fact that Email is transported in the clear is something that most people forget. I tried it this morning, and it works well.