I havent bothered for the sake of 5mbit, from past experience I have no confidence with BT's ordering system. Having had one website speed upgrade result in being billed twice for a quarter and another upgrade via phone have the order be cancelled by the system and my adsl disconnected.
Im gonna leave it alone unless they give us a big upgrade or a form like the fttc upgrade, but please post if you try for the upgrade 🙂