The hardest part of using PGP, key management, doesn't scale well in large organizations. We solved this problem at First Look Media (where there are over 200 PGP users) with GPG Sync. We maintain a keylist, and everyone subscribes to it, so everyone has the latest public key for everyone else.
I'm excited to announce that we've submitted a draft RFC that will turn GPG Sync into an internet standard!
Check this out: https://tech.firstlook.media/keylist-rfc-explainer