I too would like the ability to have forums separate from groups. I think those of us who need this are generally building very niche communities, and are not trying to create the next Facebook. Mine for example is based all around a specific era of the Ford Mustang. Nearly every topic that will be discussed on my site is relevant to every user. I don’t like the idea of any of my users, not being able to read a topic because another user created it within a private group.
On a side note: I would like the ability to retain group functions, with the ability to have forums within groups. But I would also like the ability for users to move topics between forums. This way, if some one creates a group called California Mustang Owners, and a topic is started with a question regarding Mustang Suspension, a user will be able to move that topic to the Tech section of the forums which will yield a much better return for the original poster when everyone is able to help answer his question.