On June 1st Facebook offered to encrypt Emails with PGP.
It's very important to us that the people who use Facebook feel safe and can trust that their connection to Facebook is secure
It makes sense in a way as Notifications about Posts in your Groups may contain sensitive information that you don't want your Email provider to know about.
The interesting thing about this is that the Public Key info is also available on Facebook's Graph API.
SKS Wrapper to Facebook's Graph API
The idea is pretty simple, a thin Key server could take requests from PGP clients and then look for PGP keys with the same public email address on Facebook's Graph.
Of course I don't know how many users have a public Email address on Facebook and how many use PGP but potentially it could have the great advantage that you can be sure the reach the person with the associated Facebook account, something keybase.io is also trying to achieve.