WP Social Blogroll adds a social blogroll to your blog. It will follow and display all updates of the sites in your blogroll.
See this screenshot for example.
The plugin retrieves the date of the most recent feed-item of the bookmarked site. The feeds must be indexed by Google as the plugin uses Google's free AJAX Feed API.
You no longer need a Google API Key to get it to work. If you own an API key, you can use it. But providing a key is optional.
Based on Google's information, the age of the most recent feed-item is calculated and then displayed under each bookmark in your sidebar.
Your blogroll can be sorted by the freshness of the bookmarks.
Furthermore, the title and author of the freshest post and an icon for each bookmark can be displayed.