Geshtinnanna,
I did not go and read anything on the site to which you provided a link. My comments are only in response to you as a person (believer, nonbeliever, male, female, left, right, it matters not to me) and your question.
You asked: “Do you believe that God purged the city of New Orleans to get rid of all the un Christian ways etc?.....”
I do not normally answer a question with a question and “I don't want to make any snap judgements. So I am going to ask an open and honest question”: What if He did? What, if anything, would that mean to you and would it make any difference in anyway in your life?
To me those are more interesting and pertinent questions. If we are asking ourself such questions and especially if the answers are causing changes for the better (from a God-centered point of view rather than a self-centered point of view), then I would say in that case God is using Katrina.
God is the Ultimate One at turning lemons into lemonade. The question is: Are you (we) allowing yourself to be made into sweet, delicious lemonade or are you becoming bitter seed or peeling, etc. that will eventually be discarded? If Katrina makes you think about those things then it served some good purpose and one might even refer to it as a sign from God. But I do not believe God CAUSED Katrina. Some people confuse allowance by God with causation by God.
As a student of the Bible, my answer to your question is that none of the criteria of “an act of God” or CAUSED divine punishment that are common to all past divine punishments are present in Katrina.
When He does destroy New Orleans, there will be no question about it and it will not come back!