There has been a lot of kvetching about Google Reader’s shared items feature. People say that it ‘sends their shared items sent to people in their mailbox’, which isn’t true. You need to explicitly add friends to Reader so you can see their shared items.
When you add someone to your friend list, you see their shared items in your feed list – that’s all.
Google Reader has always allowed you to share items. You have full control over which items you share and whether your shared items are public. I don’t know about everyone else but when it says your shared items are publicly accessible it means just that — everyone is able to see it. I always assumed I was sharing those items with the world.
Furthermore, not all of your items are publicly visible. You control the visibility of each tag, and only ‘shared items’ defaults to public.
Articles end up in your shared items only if you explicitly share them by clicking the ‘share’ icon on that item.
This isn’t a privacy violation. It’s a neat way to spread news.