The ability to manage the users en-masse is much appreciated. Knowing how many there are in each usergroup would be a start. The ability to mass delete all banned users would be nice. Additionally it would be nice if there are links/buttons/checkboxes to select all in list that spans over pages, so we can mass select users for management (prune from system, or move to other usergroups, etc). Further tools could include the ability to force reset user titles after updating usergroups. I have a forum with 500,000 members and they used to allow custom usertitles, this permission is revoked and resetting this to the default latter would be nice.
Having the ability to manage the content of a user would be nice as well. Instead of mass delete via spam tool, a single button to undelete any soft-deleted content would be nice.