Thankyou very much for your article, which I found very informative, and easy to follow. I had just set up GnuPG, to work with Mail among other things (via GPGMail), and the first person with whom I wanted to test this, turned out to be using the S/MIME protocol instead.
I now have both working, although I think S/MIME integrates better with Mail, since it is using its existing capability. You only have a couple of unobtrusive, small boxes at the upper-right of the window, rather than a whole bar across it. However, since both protocols will be in comparatively common use, I'm probably better off with both, than with only one.
Your article helped me to avoid the difficulties I would have had by using my current browsers (OmniWeb 5 and Safari) since they do not appear to have the certificate management capability temporarily required (although otherwise excellent). You made a rather complex and confusing process much easier to understand, and highlighted capabilities within Mail and OSX which I had evidently underused.
The postcard image is powerful: email seems so private, straight from me to you, almost instant. But in fact it is extremely public, and the sooner we become more aware of that, the more chance we have of protecting our own privacy.
Is there any likelihood that Apple will make the certificate-gaining process more transparent, more part of the OS? As a preference in Mail, for example, once you had enabled it in the Security prefs, it would be much more widely used.