I've always really disliked all forums (and other sites) where you're forced to make some first useless posts. That is I can't post where I wanted even if my account is more than a half year old. I just never had any need to post anything. When I'll be allowed to post I'll probably have forgotten what I wanted to say and thus I won't bother with that. I think better approach is just captcha solving required for posting if you're new member or something.