I've edited the post. What I meant to say is that was that there aren't many public groups yet. So, it's not like Google Groups or Yahoo Groups or Reddit which already have functioning ecosystems.
In regards to sharing discussions, the idea was that you'd be able to share discussions from any group.
Basic version: Users see an interesting post in a public group and click share. A list of these posts appear on the user's profile. You can subscribe to these posts via RSS or email.
Advanced version: Users gain the ability to follow other users and have the posts of users they follow appear in a newsfeed.
An alternative to this would be provide an activity feed (like Reddit or Quora does). Unfortunately, a stream of all of a persons activity is much less likely to be interesting than a stream of content that they have curated personally.
This feature wouldn't provide any value now. It would only become valuable once there is a healthy ecosystem of groups.