First of all, Konstantin, thanks for the great and simple plugin. Of course our secound communication to you will be for a feature request to ensure WP Approve User does not stay simple.
That said, we’re keen to have an “Declined” category so we can keep a permanent record of spam registrations (bbPress) and never let them register again. Otherwise, we might have to process and delete the same spammer five times.
We’re working on a fork in GitHub (1. to auto-generate user passwords to allow us not to send login details to be a candidate user until approval 2. to detect if the sign-up is via a successful EDD purchase in which case there is auto-approval). We could do some work on a Declined category which would mean any comments or forum posts from previously declined candidates would result in a message
I'm sorry but you are unable to post on this website.
We thought of just sending the posts and comments of Declined Users straight to trash, but in the extremely rare case that a real user has been blocked, the error message gives him/her enough notice to attempt to contact the site publisher via a contact form (no direct link) or via Twitter or via email.
We’re open to other, better ideas on what to do with Declined Users. What we know for sure is that we’d like to keep a list of Declined Users, whether that’s in the main WordPress Users table or a dedicated table.