I finally got fed up with getting emails telling me of new user registrations with email addresses like admin@pyramidscam.net (not the actual url, but similar to one), so I turned off open registration for subscribers and deleted all the ones I had. If you want a subscriber account email me (if you have my email) or use the “Contact Me” page.
In theory the contact page is bot-proof (and I haven’t gotten a single spam message from it yet), while it certainly appears that the user registration is not.