We at [Crowd Favorite](http://crowdfavorite.com) have been working with [MailChimp](http://mailchimp.com) on a slick new plugin for WordPress for a bit now. In short: it allows you to broadcast new posts to Twitter and Facebook, pulls in replies, mentions, comments and retweets, then allows visitors to log in as Facebook/Twitter identities and leave comments. This is a nice compliment to comments because it allows folks to continue the discussion elsewhere (like on Twitter, a la [Cognition](http://cognition.happycog.com/article/is-this-thing-on)) while allowing your site to remain the center of focus. You can see [Social](http://wordpress.org/extend/plugins/social/) in action here on [my site](http://wordpress.reams.me/?p=2095#comments).