I wouldn't spend the money to purchase traffic. It isn't worth the expense, if you run a good forum you should be able to get traffic with out the expense.

I just advertise my forums all over on places that allow for advertising. I also have gotten alot of affiliates around the net that have forums based on the samething I do. It doesn't cost a dime and it also shows that you are honest.

In my opinion, buying traffic is not honest, you are paying people to come to your fourm, website to make it look like you have traffic. In turn you have more traffic now, but for a forum you don't have members. So you still lose out..

You don't have to sign up with forums, you just have to see if they have an advertising board that anyone can post on. You could join forums that have something to do with what your forum is about and then just use a banner link there.

As for buying, well it really depends on the members of the places you join.

I dont think buying link is a good thing. Specially traffic method may not transparent. Probably traffic may not relevant.