Today I found Monkeysphere: http://superuser.com/questions/378853/how-to-use-gpg-and-ssh-together
For me it'd be a nice way to leverage the web of trust of GPG to have friends authenticate with my VPS. Problem: I can't find any working source for Mac OS X 10.8. It seems like it used to be part of macports, but no longer is. Neither fink nor homebrew seem to offer it either. Anyone ever got it running?