I'm glad S/MIME gets a mention because I've always been skeptical of it based on the fact that everyone rallies behind PGP.

I recently failed to install gpg2 on freebsd (for some reason it barks at me and fails and I don't care enough to waste my time on it) and decided to give S/MIME a chance with a signed cert from comodo. (which was free, just to try)

I have to say though the experience is beyond reasonable, it's very easy to get to grips with. If you're using S/MIME, I see a little verified badge in my client, not only that, if I've receieved signed mail from you, I can reply with an encrypted document that only you can decrypt.

This works with CC's and everything. The CA cargo-cult crap definitely has a benefit when it comes to web-of-trust.

(YMMV, I was using Thunderbird)