If you already subscribe to HBO via your cable or dish provider, then guess what? You will be able to watch HBO on your Xbox starting April 1st! The HBO Go app allows HBO subscribers to stream HBO shows directly through their devices, such as iPhones and iPads. And now, this app will make its way to the Xbox LIVE feature list very soon.
Personally, I don't see the point in it unless your Xbox is connected to a TV that is not connected to your cable box, but I suppose it gives you one more reason to use your Xbox for your TV pleasure.