A Google Reader Help thread has Google Reader users who are very happy with a new feature added yesterday. The feature allows the feeds you share with your friends to be commented on. You can see a detailed walk through of the feature set at the Google Reader Blog.
Here is a picture showing the comments in a Google Reader shared section:
I personally am not a heavy user of sharing feeds with friends. But I can see how this can be useful. It reminds many people about FriendFeed, who has a more public form of this sharing feature.
The Google Groups thread has a lot of happy users, but most want more. Many want integration with trackbacks, more public comments and integration with blog software.
Forum discussion at Google Groups.