I've been using postmatic on my site and it's great. Jason and the team are incredibly responsive and handled my support questions quickly. What you can do with it in terms of branding the whole user experience of your commenting is really cool. I'm sure there are more great features coming too.

When I started to jump into it more I realized how little time I was actually giving to the comment experience on my site. This actually forced me to take a step back from default WordPress and think about how the conversation with readers happens on my site. It's been a good process.