Membership Provider 2.0: Role VS Group Permission

Hi there Other developer suggest that to use Group Permission instead of Role in the application that we are going to develop. As we know that membership provider has Role provider which is defining the role of the users and I believe there is no Group permission such thing. The reason is that the Group Permission is more flexible than Role. I've notice that in the DotNetNuke (for example) it has a group permission such thing which is defined the user/group to see the page. So believe it must be apart of Membership provider unless this provider has been extended. What is your comment about this? Do you have a sample to taken this approach? Thanks ...