My forums are hobby forums. I also manage to make a little extra profit from them through advertisements so it's nice to be paid for doing something you enjoy.
I just run it as a hobby, for fun. It will never be successful and will never attract members, but I don't care. I'm more interesting in just learning how all the templates tie together and things like that. Maybe one day people will join, but I doubt it.
It's currently a hobby site and has been for the past 2 years but I'll be commercializing additional areas I just introduced which should be up and running within a month (never if left to my procrastinating ways).
I do try to make a few bucks from it but I'd consider my forum more of a hobby than a commercial interest. If I wanted more money I'd be putting my time into other things than the forum. Building forums is fun!