[quote=@UltikanaRe]
True, but '# of users that have read' could probably work.
[/quote]

But then you'd have to tag each user with every forum they've ever looked at, so it doesn't duplicate the views. Or, alternatively, saving every user who has ever viewed a topic on the topics themselves, neither of which are very efficient. Plus, it would be inaccurate if a user has multiple accounts.