There is a way of getting a basic level of association between specific blog categories and Groups by using the Blog Categories for Groups plugin, and you can make it that comments to those blogs appear as topic replies in that particular groups forum.
Compared to a platform such as Ning, the BuddyPress Group home page I feel is one area that lets BuddyPress down. By default it actually just displays the activity feed for the group. A Ning group home has extended information about the group, it has a summary of the forum posts and it has a comments section. In this article I intend to show you how by using BuddyPress Group Extras you can have a home page for your groups with all of these features.