Aggressive
captcha on registration with emailed link verification.
We do get them here as well but the community generally spots and reports them by the 3rd post so unless you're on here 24/7 you never see them.
You could require X number of posts that are moderated before a user can post without moderation. Makes too much work for the manual spammer to make it worthwhile, but, more work for the board operators as well.
I have a board related to one of our products. Nothing but 10-13 year old girls. In addition to all the other COPPA stuff we moderate each and every post. Any attempts at asking for or posting personally identifiable info is dealt with severely.