Where members have tabs for their activity stream, friends, groups, etc…there would be a new tab to display their posts.
This would behave like the normal WP loop, showing posts in all or a particular category, but showing only posts by that user.
Is that what you have in mind? I’m converting my CMS site to BuddyPress (and deep in writing migration scripts), so I’m interested in this as well. Boone’s suggestion may be the way to go; will look into it.