With BuddyPress Rate Forum Posts plugin your BuddyPress site memebrs can rate forum posts. It highlights good posts whereas poor posts are diminished. Highlighted karma points are visible for each site member. Note: The plugin is only for group forums, it is yet not compatible with BuddyPress site wide forums feature.
Screenshot showing post rating in action:
Plugin admin options page:
The plugin has many cool features, you can read about them on the plugin’s page at WordPress.org