Usually, once a moderator gets on site, they take care of all the spam. One thing you might want to do if there are multiple posts/threads from a single spammer is just report one of them and say something like "there are several from him - please delete them all" or something like that. So, one 'report' per spammer and then that hopefully cuts down on the number of reports you have to do.
Lynne - When it comes to spam I will not cut corners, And rely on the staff to take care of the spam. I like to make sure that when I report spam it's all reported even if it's by the same registrant. The reason spamming is here longer than it is is because of just that. corners and shortcuts are taken which fortunately is something I don't do in life so it's not something I do which will migrate to the forum (especially when pornographic content viewable to children) is involved.
I filed a report to vbulletin.com before I created this thread and wrote a follow up ticket after and ask yourself this. The system your applying simply isn't working because members are even having a chance to reply to such porographic threads which means it's there and no shortcuts should be taken but rather prevention and other implementations to combat this.