This plugin performs a lot of queries on front, category and archive pages.
More specifically, it performs one query per post in the page, the queries look like this:
SELECT rating_ip FROM wp_ratings WHERE rating_postid = XXX AND rating_ip = 'XX.XX.XX.XX'
While the queries themselves are not slow it adds up when you are showing hundreds of posts on an archive page.
Is it possible to perform an IN (postid1, postid2 etc) query instead? That way you could query once for all the posts.