The entertainment discount is available to anyone who purchases a entertainment book. You can order one at http://www.entertainment.com
You do not have to purchase the Orlando book, you can get the one for your hometown. Inside, there is suppose to be a an entertainment card for you to carry around for the various discounts. I'm not sure what all they consist of. I know if you plan on staying onsite at Universal Studios you should plan on buying this book because it will save you 50% off their hotels. According to everyone here on the Dis, you can't find a better price for their rooms anywhere.
Maybe someone else could tell you what other kind of discounts you could receive if you were to purchase one?