In the times of spam bots and paid spammers it would be nice to see an URL Blacklist. Or even 'Block All' feature and only allow sites from URL Whitelist.
Alternatively It can be done via disallow URLs to the first posters.
Large boards needs to take care about URL tokens and refferals (e.g. added by Amazon or Newegg Affiliate programs). Site owner is usually interested in removing tokens/refferals from URLs or replacing them.