That's a very optimistic reply. All external links here are nofollow, but it doesn't stop Spammers and other ejits trying to drop links all over the forums. :rolleyes:
If you want user-submitted content, then you need to monitor it constantly for Spam. You could, for example, set all user comments to go into a moderation queue, so that they're not displayed until you've approved them. How practical that approach is depends, of course, on the size and popularity of your site.