Lapizuli - 2:12 pm on May 29, 2010 (gmt 0)
Why not create a separate Promotional Forum dedicated to links, and only allow (non-new) members to make posts containing links in that forum? It wouldn't need to be a full mirror of the regular forums. Just a disorganized hodgepodge of a single forum, really.
A poster submits a post with a link.
The system says "Stop! Links aren't allowed on this forum. But links are allowed on the Promotional Forum. Continue posting on this forum without the link, or post there with your link."
The links could be thus "contained," as many well-intentioned spammers will just go where they're told. (Though I'm not suggesting everybody who posts a link is a spammer.)
As for the hardcore spammers who persevere (and the legit linkers who think their links are really valuable), it's true the system could be worked by a member posting to the thread without the link and saying, "check out this link over here."
But - can you do this? - you could then send clickers to a "warning" page that says the page they're about to go to may contain self-promotional links (spam), so only follow links of posters you trust, and visit at your own risk.
Plus, every time someone goes directly to the promotional forum, they could get that warning message. They could also disable the warning message if they like.
And over time, y'all would see how spammy the threads got. People could read these Promotional Forum threads and if they find them spammy, avoid them, and if not, don't avoid them. They could fade into obscurity, either as a prison/refuge for oblivious spammers, or just go away. Or, if they proved popular, there could be a merger.