Facebook "Like Button" Why it is important it add it to your site and blog

The Like button lets a user share your content with friends on Facebook. When the user clicks the Like button on your site, a story appears in the user's friends' News Feed with a link back to your website.
When your Web page represents a real-world entity, things like movies, sports teams, celebrities, and restaurants, use the Open Graph protocol to specify information about the entity. If you include Open Graph tags on your Web page, your page becomes equivalent to a Facebook page.
This means when a user clicks a Like button on your page, a connection is made between your page and the user. Your page will appear in the "Likes and Interests" section of the user's profile, and you have the ability to publish updates to the user. Your page will show up in same places that Facebook pages show up around the site (e.g. search), and you can target ads to people who like your content.
There are two Like button implementations: XFBML and Iframe. The XFBML version is more versatile, but requires use of the JavaScript SDK. The XFBML dynamically re-sizes its height according to whether there are profile pictures to display, gives you the ability (through the Javascript library) to listen for like events so that you know in real time when a user clicks the Like button, and it always gives the user the ability to add an optional comment to the like. If users do add a comment, the story published back to Facebook is given more prominence.