there are literally dozens of spam filters at the moment, during registration, when posting, etc.
when I look at the logs it really does help, 99.9% of spam attempts are prevented.
the ones that slip past the system are most likely human, so whatever we throw at them, they will bypass it.
considering that it takes us (the staff) less than 1 second to obliterate spam posts & accounts thanks to an all-powerful "spambot" button, there's no need to add further countermeasures, or we would take the risk of damaging existing forum functionality for regular users.
besides, URLs in thread titles are useless, these dont get converted as links so they arent helpful... the real spam is links within posts; but we certainly cant prevent people from posting those, this would cause trouble for regular users.