I know I haven't been here for a long time, but I still feel like adding my opinion about this:
First of all, I agree with Sideways about having clear rules. They should be understandable and not too complicated.
That said, I don't think you can be that specific because from me experience, there's a gray area when posting in a forum. The posts are somewhat spammy but spammy enough to be annoying, if you hit that, it's okay. Finding out where that area is in my experience depends on common sense and watching people who have been posting here for longer than you.
Case in point: That marine life thread: I don't get it. I honestly admit that, it seems like spam to me, but I guess it's not and I just don't get the joke. I won't post in it, problem solved.
That said, I also post at another message board which is pretty spam free. The reasons for this in my opinion are three things:
1. Everything can be discussed but check whether there's a thread about this already. If there is, use that and discuss your problem there (we have one for politics and relationships for example, even a general spam thread (though it's really just little discussions that don't warrant opening a new thrad, actual spam gets you banned), a car thread and so on). Only if you feel that your thread is about a new topic and interesting enough, you can post it.
If you post something that's either considered useless or fits into an existing thread already, your thread will get closed along with a link to the existing thread or a short explanation. If you do it again, you get banned. Simple as that.
2. Coherent, intelligent and respectful posts: If you're going to have discussions about touchy subjects (politics, religion, relationships), you need strict rules. If someone is posting populistic bullshit or insulting people, he will get banned. This rule is enforced pretty strictly, I've seen people getting banned that were really popular and had posted there for over 3 years. But they knew the rules and chose to violate them, so they got banned.
3. Chatting on a forum gets you banned or at least the thread gets closed. There's IRC, IM or PM for that. Don't do it in a thread.
What I'm trying to say is: I feel a forum is a lot more useable and friendly if you only have a couple of threads where discussions about these things go. And if the rule "only open a thread if you deem it valuable" is enforced, the spam dies pretty quickly, because interrupting a thread with stupid spam is a lot harder to pull off (either people keep the discussion going or at least you have to be more of an idiot to do it) than creating a new thread to spam in.
And if you don't feel like discussing certain topics, you can easily avoid the specific thread adressing them and additional threads about the same topic won't spam up your forum. It's just one thread.
I think everything can be discussed on a forum as well, even touchy subjects, as long as people adhere to the rules. Then it can be quite fun.
I know this is against Jeph's opinion but I think it doesn't hurt to suggest it, it's not like I'm forcing him to do it (not that I could anyway).
Edit: Before people yell at me: These are only suggestions. They are not meant as accusations ore personal attacks, just things that I think might improve this forum.
