Google has added a new feature “Friends list” within Google Reader (separate from your Gmail chat contacts) for making sharing more flexible and to let you manage and choose who to share with. To get started, you can choose to either continue sharing with all of your chat buddies or create a custom Friends list with those that you hand-select. People that you add to the Friends list will be able to automatically see your shared items in Reader (remember, shared items always have a public URL).
Google has also made it easy to manage who shares with you. When someone decides to share with you, you will get a notification and the ability to preview and subscribe to their shared items. At that time, you can also choose to share your items with them (or not).