Is there a setting to keep users from posting links until they have reached a certain post threshold?
Users with less then 10 posts cannot post a link, for instance.
At least not in stock code.
They could just manually type say msn.com or http://www.msn.com
You can limit their ability to use certain features like ubb code, signatures,attachments. etc. Or moderate their posts until they reach a certain post count and then they are automatically promoted to a group that is not required to be moderated.