Nice implementation but shares the same issues as PGP/GPG system in that it's a rather closed system, requiring installation of the same software by the other party. Agree with the previous poster that S/MIME standard and certificates are much easier for the majority as S/MIME support is built-in eg. Mail.app, Entourage etc. I would recommend Thawte.com as the source for your free certificates (just like those in your browsers for https).

If I were PGP I would be worried - this is a very good implementation of transparent email signing and encrypting. Keys are generated once for each email address and stored on a central server and Ciphire sits between email package and server and intercepts the SMTP stream; if a recipient's keys are found the email is signed and encrypted, otherwise it is signed only, and decryption happens at the far end if required. There is no user interaction in normal use and no need to configure the email package (so any package can be used) - even the initial key generation and signing only requires one password and one email receipt. The sole indication that Ciphire is doing something is an animated envelope icon in the Menu Bar.

The only minor problems are that the UI of the various Preference windows is not quite compliant with the Apple guidelines - although it is close - and that, by default, received email has "[c]" or "[u]" ("ciphire" or "unrecognised") appended to the Subject: line to denote the sender's status, although that can be turned off; I would prefer an extra mail header.