One of the check-boxes on my resumé to-do list for 2014 was to publish a decent plugin from scratch on the WordPress repository. This is my first entry of the year (er, well,of next year I guess... LOL).
Anyone who has run a WordPress site for more than a few weeks knows that 95% of all site registrations typically come from spammers. When they can't get a comment approved, they just sit in the database, clogging up the works.
We call these folks Zombie users, and they're coming for your brains.
This is a plugin designed to do one thing: clean up zombie users.
If you have a WordPress site with lots spammer registrations, this plugin will delete any user who has never had a post or comment approved. Zombie Users... BRAAAAINS.
A word of warning, DO NOT USE THIS PLUGIN with MarketPress (I suspect Membership would be ok). I haven't yet tested it in environments where a user might be deleted who has purchases but not comments or posts.