[munin]

you can revoke your S/MIME key from a CA (you just need to remember the revocation password you gave them)

S/MIME is also built in to (almost) every thick MUA. it works on iOS out of the box, it works in outlook, thunderbird, mail.app and mutt out of the box.

once you generate a S/MIME cert through a big provider, none of the other big providers will give you an e-mail cert for the email issued by the other big provider (probably, still trusting them to do the right thing).

[joshuak]

No, you cannot revoke your s/mime cert. Your CA can. That is a big difference.