I have been an atheist for may years now. However, it never occurred to me to actually formally cut my ties with the Catholic Church by making a formal declaration of defection. And I wouldn't have known how to do it or even whether it was actually possible to do it in a formal way. But I have now discovered that there is such a formal proces: the ACTUS FORMALIS DEFECTIONIS AB ECCLESIA CATHOLICA. A website has been started from where you can download a form to send to the diocese in which you were baptised. You can get it here: http://www.countmeout.ie/ . I have just downloaded and filled mine in ready to post on Monday.
You may think that formally defecting is a pointless exercise, especially if you haven't had contact witht the church for years. But consider this: you name remains on the register and the church can, and routinely does, count on your apparent continued allegiance when quoting membership statistics. This enables it to artifically shore up its authority. This practise is especially pernicious when it uses its falsely infalted membership statistics to oppose legislative changes on issues such as gay rights, abortion, euthanasia, contraception and divorce.
When you send the form in you will get a letter back asking you to respond before the defection can take effect. This is your chance to tell the church why you are leaving. I think the church needs to hear this, whether your reasons are to do with child sexual abuse by clergy or the church's so called 'teaching' on matters that promote inequality and injustice such as it's discrimination against women and gay people and its role in spreading aids becasue of its refusal to allow catholics to use condoms.
I would love to know how many from this site are brave enough and confident enough in their atheism to actually take the step and burn your imaginary bridges with this organisation.
Where this especially matters is in the case of countries where churches receive government funding based on their membership count. In those cases, if you don't renounce your membership, the church continues to get taxpayer money because of your membership.
This doesn't apply to the US, obviously, but as the URL in the OP hinted at, it's a big issue in Ireland.