I always do my own seasoning even on the pre-seasoned cookware. I have an Emeralware dutch oven that was pre-seasoned, but I seasoned it anyway (just like Phatch suggested) and haven't had an issue even after cooking chili and spagetti sauces. I always re-season new cast iron after cooking and cleaning something acidic, actually after cooking anything in new cast iron as IMHO for proper seasoning to take it takes a year or more. I don't do the 500 degree, but I hand dry, coat with a thin coat of oil and put it in the oven at 350 for an hour, turn off the oven and let the pan slowly cool down over-night. I'm probably being OC about it but I've not had any issues with my cast iron...yet.
