This extension is based Danny Douglas’s  SocialBookmarks Extension. I suggest that you also have a look at it.

What is AddThis?

AddThis is one of the popular(actually #1 per their site) social bookmarking button on Internet. This button eases your burden of maintaining links to each and every social bookmarking site on internet. Instead, the site provides us with a code that, once embedded into your post, opens a small popup with number of ways for sharing your content. Also, it tracks all the bookmarks through which you can analyze.

What AddThis extension does?

Instead of manually embedding the code, provided by AddThis, to each and every post, this extension inserts the code, on the fly, as and when the posts are requested.

How to insall this extension?

• Download the extension from the bottom of this post.
• Extract the AddThis.cs and upload it to your BlogEngine.Net’s ~/App_Code/Extensions folder. If your blog isn’t hosted on root, please change the path as needed.
• Goto Settings and select Extensions tab.
• Look for AddThis under the Name column and click on Edit link on the same row.

• In the next page, change the Username to your own AddThis Username so that you can track your traffic.

• Check Only Full Post  if you want to show the AddThis button when a full post is requested. If you want to show the AddThis button on all post on the default page(as request by Chad), just uncheck it.
• Now, you should be able to see the AddThis button at the bottom of your posts. 

New features in v1.3

• If you don’t wish to monitor your bookmark traffic, just check the Keep Anonymous option and your traffic will not be monitored.
• Now you can choose from multiple buttons supported by AddThis. The details on how to use different button is given in the inside help, on settings page. If you are struck anywhere, just leave a comment. You can see the list of possible buttons here

• I’ve also added a simple option to change between small and large buttons. Check Large Button option to show large buttons. This will not apply to plus button.

Your comments, compliments and bug reports are always welcomed…

Download here --