I like the idea of a 1 post limit if the first post is spam, but a queue could force a useful new contributor to wait until a moderator or curator is next online. Also, a flood of new users would mean all of them are limited to 1 post until they reach the front of the queue.

What if we use all the users rather than just moderators and curators? Instead of a queue, just prevent a user from posting if they have an open spam flag. Possibly only counting flags from users who registered before the flagged user, to avoid spammers using this in reverse to block others from posting?

At a quiet time a spammer might still be able to post their daily limit in quick succession. I'm not sure how to avoid that without a queue. Maybe a compromise could be to limit to 1 post per hour for the first post?

The problem with "more aggressive limit only if the first post is spam" is that spammers are the ones most likely to try multiple posts in quick succession, before the first one can be flagged.

While Karl is correct, I think Lundin must have gotten a flag in before the spammer finished their bombing run.

I like Trich's idea, but we should weigh the possibility of a malicious existing user DOSing someone else. Maybe our old friend Wilson Score is a part of this?