From the Gmail Blog:
Today we’re retiring the old version and excited to be bringing the new Google Groups to everyone. If you haven’t tried Groups in a while you’ll notice improved options for managing your groups and long time users may be surprised by all the features we have added along the way.
One of the recently improved features is the ability to create an inbox that allows you to collaboratively share, distribute and track responsibilities with others. Imagine you and a few friends are organizing an event for your school and want a single email address to coordinate with vendors, parents, and volunteers. Members of the group can work together to manage email, assign items to each other, and mark items resolved. This can be a great feature for teams seeking a really simple way to get things done without sharing passwords or losing track.
Read the Complete Blog Post, Screenshots
Guide to the New Google Groups