The problem with the mayor and governor's inaction was that it prevented the evacuation of those without the ability to evacuate. There are people without money, without vehicles to travel. Instead of being able to get those people out on some form of public transportation, the failure to act has put them in a last ditch effort to stay alive by riding out the storm in the Superdome.
When the mayor and governor have to be told by the President that they need to evacuate their cities, something is seriously rotten in that state's chain of command. Crucial hours were lost because that mayor was consulting with lawyers over the legalities of trying to save lives. I think there's plenty of blame to lay at their feet.
Three, maybe four areas of strong localized shear offshore in this image (green and red close together, potential tornadoes):
http://www.intellicast.com/Local/USLocalWide.asp?loc=klix&seg=LocalWeather&prodgrp=RadarImagery&product=RadialVelocity&prodnav=none
What sort of public transportation could New Orleans mustered to move 100,000 people in 18 hours? Others have suggested totally unrealistic ideas such as steam boats and C-130s.
The guys may not have made the best decision, but these decisions aren't as easy as many are making them out to be. We go through this all the time everytime something happens in this country and the democrats start yelling "Bush had not plan" or "Rumsfeld should have anticipated this".