Yes, it would be easy to control it using user groups.
You just have to be a little imaginative.

I guess the problem for some people is that they started their forums with the intentions of letting everything be free. Then they realized like everyone else in the "physical" world already knows that you can't keep giving away something for free without *someone* paying the price.

But their user groups are based on other things already like number of posts and other stuff so it is hard for them to switch over to paid and unpaid memberships based on usergroups.

If you are just starting your forum, then paid memberships is the way to go. If you currently have forums, then you are going to have to make a hard decision...

People realize that if you pay for something you will get something of higher value than if it were free.
Hey, just look at all the free discussion forum software and compare it to vbulletin! Jelsoft doesn't give vbulletin away for free does it?