Google Reader's sharing feature was barely noticed when it was added, then it got more exposure when the shared items started to be broadcasted to Google Talk contacts and some sites aggregated shared posts. As Google Reader became more social, people discovered that it has some important limitations. "Have you ever wanted to share something that you were reading, but you didn't want to go through the hassle of subscribing to a whole feed for a single interesting article? And what about sharing content from sites with no feeds?, " asks Google Reader Blog.
Google Reader finally added an option to share any web page and to add notes for each shared item. Next to each post, there's a new action: share with note that can be used to explain why you found the post interesting or to add your comments. You can also go to the new Notes section to add a note or drag a bookmarklet to your browser's link bar so you can share any web pages, even if it doesn't have feeds.
Another improvement is that Google Reader shows small avatars next to each shared item and you can customize your public page by selecting a theme. But don't get to excited as the three themes that are available (ice cream, ninjas, sea) fail to impress and look terrible in Internet Explorer 7.
{ Thank you, Josh, Myo, Pascal. }
Later notes:
* you can't delete or edit notes
* there's no keyboard shortcut for "sharing with notes"
* when you share a post, Google Reader displays the full content of the post in an editable box. That means you can modify a post before sharing it. And that's not all: Google Reader shows the HTML code when you click on the editable box
* there's an overlap between this feature and services like Google Notebook or Google Shared Stuff.