I have seen this in action already on another site, I am just not sure whether it is a buddypress site or even a wordpress thing.
All the evidence looks like it is as it has activity/groups, etc but it is a privately built website so not sure.
http://www.rvillage.com is the site and the accounts are free if anyone as 5 mins to go and have a look at the explore page on the site. This is the page that has the functionality
I have just found that out. Which is that Buddypress uses BBpress. I have also been given a youtube link to a guy who has explained it well, so if anyone else asks the same/similar question here is that link
