A Louisiana State University expert on levies says that Gustav is likely to hit never-tested levies to the South of New Orleans. These levies are of the same build as those that broke in 2005 when Hurricane Katrinia struck. Storm models show that Gustav has the potential to bring about water levels and wave action that could breach these levies. Levy upgrades were not scheduled for completion until 2011.
Another expert noted one positive development since Katrina: pump-houses have been raised onto elevated platforms. "This time we won't have to evacuate the guys who run the pump," he said. Brilliant.
I have posted a beautiful and rare map of the levies of New Orleans here.