Recently Facebook added new functionality of commenting on Websites with Facebook account. Visitors of Website can add comment on website with their facebook account and this story will posted on his facebook profile with link of that webpage....
You might have seen such comment box on different Websites like MTV India, some tech blogs ,etc....
To Add such comment box to your website/blog, please implement following steps
1. First of all go to Facebook Developers : Comment box
2. Write your blog/Website's URL in box below "URL to comment on" (by default example.com is written over here, change it to your website's URL)
3. Change "Number of Posts" and "Width" according to your requirement
4. Click on "Get Code" and copy that Code
5. Now go to Design---> Page Elements
6. Click on "Add a gadget" and select HTML Javascript
7. Now paste that code here and click save
8. All set.... You will find Comment box on your blog..
(Don't Forget to comment on this page with your Facebook account)