Lafourche Parish (where I live) president, Charlotte Randolph, has issued a "mandatory evacuation order". The order does not mean that you must go or they will drag you out of your house. You may stay, but no emergency services will be provided for you. Of course, everyone should evacuate, but this is part "cover our asses" coming from the powers, because I know, and they know, that a number of folks are staying, including my two sons, and the parish authorities will be forced to provide emergency services to those who remain here.
I don't think my sons are wise, but one has three basset hounds, and the other has four cats, so you can see their reasons. Their families won't be with them, just the pets, which I assure you they will not leave behind if they decide to evacuate after all. My son who lives in Houma will come to stay at our house in Thibodaux, which is further away from the Gulf of Mexico. We live in the higher part of Lafourche Parish
In lower Lafourche and Terrebonne Parishes, there will be flooding from the storm surge, no matter where Gustav lands, so those folks have already or will soon move out - I hope.