Google Reader added a new feature that lets you share posts in other services: Twitter, Facebook, Digg. The feature is opt-in, so you need to go to the settings page, click on the "Send to" tab and pick your favorite services.
After selecting an item, use the keyboard shortcut Shift+T to quickly open the "send to" menu. Google Reader opens a new tab when you choose one of the "send to" options and most of the necessary information it's already pre-filled.
If your favorite service is not included in Google Reader's list, you can add it from the settings page by clicking on "Create a custom link". Here's how to add a "send to" option for Google Bookmarks.
Name: Google Bookmarks
Icon URL: http://www.google.com/favicon.ico
And here's how to use AddToAny, a service that lets you select between many social sites.
Name: Add to Any
Icon URL: http://www.addtoany.com/favicon.ico
Google Reader added two other options: you can now subscribe to sites added to your contacts' profiles and mark as read items older than a day, a week or two weeks. The second option is useful if you have a lot of unread items and you only want to read the recent news. As you probably know, Google Reader automatically marks as read the items that are older than a month and this can't be changed.