Super module. Seems to leave custom fields in the database though. I ran a successful import with extended fields using UIF Plus. After forgetting to remove this module it purged them all (as expected) so I tried the import again. Now I get integrity constraint violations, so I looked into the custom field tables and sure enough - all 8,000 deleted users' fields are still in there.

I'm not 100% sure if there's a routine that will eventually purge orphaned records such as these, but seems like deleting them when the users are nuked would be in order?