I have about 30 followers on Reader and I follow a similar number of people. We subscribe to feeds from a bunch of scientific journals and different sections of the arXiv. When we see a paper of interest (or a comically bad paper), we share it. The discussions (private within our approved group) are sometimes quite long and detailed (e.g. 10 pages worth of content in 40 comments). A fair number of collaborations and new papers were born on Reader. I probably see about 100 items per day in my Reader feeds, share a couple, and write a page or two worth of comments. At present, G+ does not keep track of which items I have seen so the interface is not in any way competitive.

I would prefer an integration of G+ circles with sharing preferences on Reader, but I don't want to give up the Reader interface for the much less utilitarian G+ interface. I'll wait and see what this change brings.