Facebook now commands over 500 million users and cannot be ignored as a great opportunity for any business. Facebook pages give you the ability to recieve feedback from customers, inform them of news and new products.
Posting news and product information to facebook can even be done from your blog, so there is no need to post content twice.
Facebook apps and plugins can be used to bring content from facebook right into your website. This can show that you have an active client base and are actively engaged with your customers. It can be a simple as a humble "like" button or as complex as a fully fledged custom built application.
For example, over on the right of this page you may notice a facebook plugin showing content pulled directly from our facebook page. Anything posted there will show up here almost instantly. There is also a "like" button at the bottom of this page. Go on give it a click!