I don't know if this is a known issue, or I've somehow managed to screw something up, but it appears that PGP/GPG signed e-mails (email@example.com) that are sent as journal entry submissions aren't being processed.
My mail server shows that the e-mail was successfully accepted. But nothing displays in my journal. Sending an identical e-mail using the 'PIN' authentication (user+PIN@post.livejournal.com) works without issue, and the journal entry displayed within a few moments.
The PGP signed post was tried twice, without success. And it was working great for me in the past, as recently as 'Wed, 10 Dec 2003 21:00:25 -0600' (my last e-mail post that was PGP signed and went through). I've verified that my last successful PGP signed post e-mail was sent to the same e-mail address and signed with the same key as the recent failed PGP signed post e-mail.
Thanks for your time. If anyone needs any additional information from me on this, just let me know.