a new site where a 'badge' or goal could be defined by the user with
the aggregation site would read activitystreams from users and determine if the actions in that stream qualify them for any of the defined badges. the participating sites would need to provide an activitystream for each user. the aggregation site would provide a reputation document or list of earned badges.
a site could make use of badges earned from other sites, or look at more general badges that the aggregation site itself defines.