Released this past Friday, Jetpack (an Automattic plugin) now features Jetpack Comments. This is a very positive step up from the default comment system that comes with WordPress as this allows site visitors who wish to leave a comment using one of their social networks as a registration, eliminating the need to create yet another new account/profile. Visitors can now leave a comment as a guest, or can choose to use their WordPress.com, Twitter or Facebook accounts to identify themselves.
Great feature add to a plugin that is continually showing signs of improvement and helping WordPress users get the most out of their site!!