We can add a Facebook App Tab to your Facebook page so you can ask your Fans to join your list. Imagine if your page was deleted or hacked and you had to start all over again? If you have been encouraging your Fans to join your email list all along you will have a means of contacting them independantly of Facebook. Don't risk all your hard work.
Having a subscribe tab on Facebook also gives you a great means for fans to enter your competitions. How about this post 'Join our email list today via our tab above to have the chance to win a ....'