A TRUE Dutch Oven is cast iron - it has 3 short legs on the bottom and a flat lid with a lip so the coals don't slide off the top. The term, in modern usage, has been basterdized to mean just about any pot with a lid that has a large diameter, short sides, and 5-8 quarts in size.
The enameled cast iron pots make by Le Cruset are "technically" French Ovens.
From my experiences growing up cooking in properly seasoned cast iron .... it is not reactive and you don't get any "funky" metalic taste when making something even as acidic as chili. The seasoning is a layer of polamorized oil which provides a non-reactive barrier between the metal and the food, similar to the enamel layer on top of the cast iron in Le Cruset. The thing is to not store it in cast iron.
"It ain't what you don't know that gets you in trouble. It's what you know for sure that just ain't so." - Mark Twain