Google Reader users can now leave comments on shared items. Google has introduced it as a way to have a discussion with friends outside of a site's main commenting system, and specific just to that shared item and their group of contacts.
To help manage this new stream of information, Google Reader now has a filter that shows you the latest conversations in one place. Here you can view all the latest chatter, and continue to add more comments just like a forum.
In addition to reading and adding comments through Google Reader in your computer's browser it also works on Reader's iPhone version.
It's all very much like FriendFeed, although the privacy it a bit tighter since only friends of the person who shared the item can see what was said. Another limitation is that comments are limited to the friends' shared items section of Reader, however Google says it will be making its way to the "all items" section of user's feeds in a later release.
On the surface this may seem like a very small feature. But if Google were to open up the commenting threads to all Reader users, regardless of their friendship, and enable publishers to feed these Reader comments into their own blog comments, it could make Reader more than just a feed catcher the same way FriendFeed has enabled blogs to suck in the conversation that's happening outside of their own pages.