Just as it's too early to say with confidence what caused the death of de Menezes - though I sure as hell want to know - it's too early to say what, if anything, really went wrong in New Orleans.
I don't think it's too soon to draw some general lessons, however.
This article in the NRO alleges the following (my emphasis):
... a working group decided that the workable solution to the problem of thousands of stranded citizens was to ask churches to set up a giant car-pool system. The plan further called for a DVD to get the word out, which was still in production when Katrina struck. A cynic might say that such a plan was drafted so city officials could say they had a real evacuation plan, written down on official letterhead and signed and announced and all of the other things that make bureaucrats swoon, but was in point of fact yet another exercise in passing the buck to the next schmuck to occupy the conference-table chair. Again, at this point I would treat this as an unconfirmed allegation, but anyone who has had the "disaster recovery" duty dumped on them in a business is likely to see it as at least plausible. The general lesson is that, if you might someday be dependent on an organisation's disaster plan, it would be a good idea to find out in advance what it is, and whether it makes any sense. That's the only way to be sure it isn't an exercise in pointless box-ticking.
Everyone should do this, everywhere. Make a list of, say, the three most likely disasters to hit your area. Find out what the contingency plans are. If they're stupid, make a fuss. In any case, make your own plans.
And, of course, get risks in perspective. It's silly to be planning for the likes of a nuclear strike, if you haven't planned for a house fire. House fires kill 700 people a year in the UK. That's a 7th of July death-toll every month.