Google Reader made some improvements to give you more sharing control and help you easily find other people's publicly shared items.
-Using new Google profiles-powered people search feature, you can now find people with public shared items and subscribe to their shared items with one click. Bowse by name, location, or topic, and start following new people.
-You can now share items with a specific group or with multiple groups, with this only people you add will be able to see and comment. These’re same groups from your Gmail contacts -- so, changes made in Reader will change them in Gmail as well.
-When you check the box marked "Add a link to my Google profile," anyone using the search feature within Reader will be able to find and follow your shared items. You can also give Reader shared items page a custom URL that uses your Google username, like www.google.com/reader/shared/pink.black. You need to enable this under "Profile URL" on your Google profile first.
-With a quick click of mouse (or swiping "L" key), you can "like" any item in Reader. All "likes" are public, so anyone reading an item you've "liked" in Reader can see that you're a fan.
-Although your shared items might be public (and publicly discoverable), only people you’ve added to a sharing group will be able to comment on them.