WordPress gives us the ability to flag a comment as spam banishing the poster to infamy.
Why not provide the same feature for user registration as well? I have a user who keeps registering on my blog. It is a spammer who keeps re-registering after I delete the registration. I recently decided to change their password, but that will not last long.
I do not want to force people to register to read the blog. I may have to resort to kaptchas. The simplest solution is for WordPress to allow us to flag the user as spam banishing them into the bowels of wherever forever.