There is a solution to his particular problem: better forum software.
I don't want to trivialize the problem of writing spam-resistant forum software but it's not such an insurmontable problem (this forum being a proof positive for that).
For the reference: I've been running a fairly popular forum (http://forums.fofou.org/sumatrapdf) for several years, using forum software that I wrote.
I don't even require the user to log in, I don't require moderation for posts and yet I had zero automatic spam (I attribute this to my unusual captcha http://blog.kowalczyk.info/article/16fw/Best-captcha-is-exot...).
I occasionally get human spam i.e. someone writes a post with the only purpose of linking to some other website. I just hellban them after I see the post in my rss reader.
And I didn't even write any special anti-spam code (other than hell-banning), because I'm lazy. I can easily come up with simple ideas e.g. putting all posts that contain links in moderation queue.
To reiterate: his problems were caused by a crappy forum software that didn't do much to protect from seo spam.
I don't really know how current best off-the-shelf forums fare in this respect.
I would rather not spend my time maintaining my own forum software so I have high hopes for http://www.discourse.org. I'm sure StackOverflow had plenty of spam problems so discourse people should understand the problem.