We are adding comment ratings to our FV Thoughtful Comments at the request of one of our clients. He likes Disqus features but doesn't like entrusting his user generated content to a third party service and doesn't like Disqus page load slowdowns. A very smart guy and successful publisher.
We've experimented with Epoch and wpDisquz and have even donated to the latter. Unfortunately wpDisquz is not fast enough either on a really busy site (measured in both page views and frequency of comments).