[Jurg]

My simple solution is to moderate all posts from new members. You then create a usergroup which doesn't require moderation of posts, and set up auto-promotions so users with at least x posts (mine is at 10 but 1 will do) get promoted to this new group. I have not seen a spammer yet on my forum whose first post wasn't blatant spam.

All you need to do is moderate one (or however many you want) post per new member. You don't even have to mess with their settings as the auto-promotion will do the work for you. This is the least labour-intensive way I've found for keeping users from seeing spam, and it works.

BTW lose the "admin to moderate new accounts" option, it is useless. As you said, unless you know the email address of every potential legitimate new user, you're just wasting your time.