By organizing your contacts into Groups, you can easily see updates from social networks, send mass texts, or mass e-mails in WP7. Windows Phone 8 looks to be expanding on that functionality by bringing back our old friend from the 90s: chat rooms. This info was pulled from a dll file found in the WP8 SDK:
The "private room" idea is a pretty interesting one, and one that could be pretty useful... as long as it doesn't require everyone to have a Windows Phone. We don't expect Microsoft to lock it in like that, but group chat will need some sort of common platform, so it would make sense if everyone has to be on Facebook or Windows Live. The private room idea actually sounds a lot like what Google is doing with Hangouts, just without the killer feature of group video chat, but Microsoft does have Skype which can do group video, so we'll see. We're definitely excited to hear more about this.