Well it depends how many of your users have 'weak' (i.e. crackable in a reasonable time-frame) passwords I guess. Their savvy-ness will probably vary depending on the nature of the site in question.
But fair enough, let's just slap people around the head until they adhere to good password...
By the time they're reading the hashes from the database then you're already compromised so it's not really the biggest concern for whoever is running the forum. Realistically though, are attackers going to expend serious effort (assuming a not-totally-useless algorithm + salting) cracking every...