It uses a lot of template hooks rather than the Template Modification System, and the killer is likely how it counts ratings is particularly heavy on the DB.
@Luke Foreman doesn't have it using a cached field on a per-user row. Instead it runs SQL to count per rating per user totals everytime someone looks at a user member card:
Code:
(select sum(count_received) from dark_postrating_count where user_id = user.user_id and rating in (".implode(",", $positive).")) as positive_rating_count,
This isn't as bad as counting every instance of the rating, but it could be better.
:edit: Looking closer, it doesn't do much caching of the ratings list like stock XF does when reading the post, so it is recomputing the list of Ratings per post each time. Ultimately it is adding a bunch of joins and calculations rather than reading a pre-computed list for a post's ratings.