I have worked with Group Chat for some time and it was always a love/hate affair. What the product offered was well understood and when used right helped reduce the need for email. The downside was the solution was difficult to install and manage (this is being polite <grin>). The release of Lync 2013 is pending and Group Chat gets a real upgrade becoming Persistent Chat in name. This time around I played more with the client experience as it is now part of the Lync 2013 client but have not worked on the admin side of the feature.
See this post on Next Hop to read more on the new feature - http://blogs.technet.com/b/nexthop/archive/2012/08/28/lync-server-13-preview-what-s-new-in-persistent-chat-server.aspx