Published 28th January 2009
Quite a few things happened since I wrote the GnuPG for Mail.app in Leopard how to, so I thought it would be time for a little update:

If you want to install GPGMail but don't have GnuPG
installed, just pick up MacGPG2 and everything should work fine.
If you already have GnuPG installed and don't want to have a second version on your system,
just install Pinentry-mac and specify the path to the application in
~/.gnupg/gpg-agent.conf:
pinentry-program /usr/local/libexec/pinentry-mac.app/Contents/MacOS/pinentry-mac
If the password dialog is annoying you, check out this guide on how to install gpg-agent with MacPorts on OS X.