As of the addition of the Brewing Stand, the cauldron has become mostly useless, as far as I can tell. They can, however, still hold water. I think they should be able to create larger amounts, and varied flavors of stew or soup. Basically, you put a netherrack block under a cauldron and light it (need to switch some things so it doesn't go out and it doesn't just burn the cauldron), and then fill the cauldron with water. After it is full of water and heating, you start tossing in ingredients with 'Q'. This will get rid of the item, so you can't reuse them, and it changes the color of the water in the cauldron. Basic ingredients are as follows:
Cookeded/Raw , Chicken/Beef: Adds to stew taken from cauldron later.
Cooked/Raw , Pork/Fish: Adds to stew taken from cauldron later.
Pumpkin: Adds to stew taken from cauldron later.
Red/Brown Mushrooms: Adds to stew taken from cauldron later.
Rotten Flesh: Adds to stew taken from cauldron later. However, also makes you sick when you drink it.
The cap for hunger regained will be
After you are happy with your stew, you can take out bowlfuls by right clicking with a wooden bowl to fill it up. Each cauldronful gives you 8 bowls of stew. This may have been suggested before, but I couldn't find it with the search bar.