FriendFeed is the new Twitter. That's what everyone is saying these days (including me). And by everyone, we mean the early adopter crowd, many of which that made Twitter popular in the first place.
Interestingly, one of the most common things to see on FriendFeed is a long back-and-forth conversation develop from a simple, short Twitter post. Given the uzi-fire rate at which the FriendFeed team creates new features, it was only a matter of time before they decided to create the ability to send some of those conversations on back to Twitter.
There has been a lot of conversation in the circle of folks that dips into my FriendFeed stream regularly on the topic of comment and discussion fragmentation, which essentially means the problem of posting things on your blog, them ending up in your lifestream at Twitter and FriendFeed, and the ensuing conversation never making it back to the original posting place. This little bit of functionality actually re-unites a bit of the conversation from the FriendFeed fragment (shard?).