Due to the ridiculously high number of attempted spammer registrations, the ability to self-register a username for this blog has been removed.
An approval system for new registration was already in place, and very effective. However, the huge volume combined with my limited time means that I can no longer deal with the administration for the approvals and/or rejections.
If genuine users wish to register for a blog login, then they can send me an email message. If everything looks reasonable, I will happily do a manual registration.