The main feature is of this release is the extensive use of Bootstrap and Sass in the views. The views are decoupled from the style. This means you should be able to completely change the style of your social network without touching the HTML.
Besides, the look and feel of our site has been redesigned, including a Get started guide to put things easier to new-comers to Social Stream.
There is a complete guide on Upgrading to Social Stream 2.0 to facilitate transitions from Social Stream 1.0.
We hope you enjoy this version as much as we have.