I had not previously tested rigorously enough the process of registering to post comments, and I suspect that the email notices containing initial passwords were not being delivered due to the nonstandard MTA I have running. I switched the SMTP settings around and it should now complete the registration process. In case, you know, that was why anyone was waiting.

[Edit: Okay, that worked only for local accounts, which is of marginal use given that no one else has accounts on that server. With Atuarre's guidance, I tore out the supplemental SMTP module which was munging relay headers and thus causing peer rejects, and just symlinked the standard bin/sbin shims provided with the MTA. I had previously only changed the hardcoded sendmail path, but the script must prefer mail() over sendmail() so it would have still been hitting a bound port conflict.]