Nothing creates a happier user base than mandatory fees. Just my advice.
There's nothing mandatory about offering a donate feature on the forum to complement the sell off of ad space like this forum does (which is also optional by the way).This forum did very well as I can see myself using that method, so I figured I'd adapt this, to my forum to get things moving along.Payment is never mandatory on my forum and it never will be.
Or are you suggesting some kind of membership fee?