Somehow I had acquired 889 user accounts... I went through and removed 869 accounts - which leaves us with the 20 original legitimate accounts (though the forum is still reporting more than that - will need to look into that later).
I think I did a pretty good job at removing only the spam accounts. If you had a legitimate account and it was deleted - sorry about that!
The forum & my blog will need to have their login/registration process reviewed & hardened. Don't be surprised if you see changes in the coming days/weeks.