At the moment the economic elements of the game are basically a cliff-edge. At the beginning the economic needs of your dwarves are paramount, you are preoccupied with getting them food, drinks, furniture, clothing and weapons-grade metal. Once you have those things the economic game is essentially over, the dwarves are perpetually happy and the only real economic demand in the game is what the player happens to arbitrarily want in their fortress.
This is all despite both the existence of a complex system of personal likes and dislikes as well as the presence of a number of unused consumer goods, musical instruments, toys, crafts etc..
Dynamic Consumer Demand
Citizens have a list of demands written in their personality screen. To start with these are only the requirements that presently are there, the position requirements of the individual as well as for food, drink (only for alcohol dependent creatures), bedding and clothing. As these initial demands are met new demands are gradually added based upon what the individual personality happens to want. If these demands are met then gradually new demands are added but if demands are not met then they cause unhappiness.
Personality effects things as well, Greed causes people to more quickly want things based upon their personality when their present demands are met. Envy on the other hand causes them to more quickly gain negative moods when other dwarves that share their demand have their demand met but not them.
Shops
Unlike at the moment where dwarves simply consume items from the common stockpile, dwarves instead 'privatize' items from the common stockpile before consuming them, wearing them or appropriating them, depending on the type. Essentially this does not change much, but it provides the basis for the system as the privatizing of the items meet the dwarves demand for those items.
In order to control production and determine the total consumer demand of a large group you would build a shop. A shop develops the appraise labor, making it serve as a means to train future brokers for your fortress. The downside is that each shop permanently ties down someone in order to man it, thus using up quite a lot of labor hours.
If a dwarf has a consumer demand that they cannot meet from the common stockpiles they will put an order in for it, allowing a player to economically plan to meet those demands. Thus the shop is useful even for the most 'communist' fort. However that is not all the shop does, it also can be used to ration and to sell items.
Rationing is always possible at the shop. Rationing restricts the amount a given dwarf is allowed to own outright and/or the amount they are allowed to acquire of an item per a given time period, the former is more useful for non-consumables, the latter is for consumables. Items that are rationed cannot be taken freely from the stockpiles, instead they must be acquired from the shop itself. The shop tries to keep a certain stock of a rationed item and haulers will bring it those items, the shop can store a certain amount and then it deposits the items on nearby squares and the shopkeeper fetches the item for the customer.
Idleness
Citizens would continue to work for free as the do at the moment. However they randomly succumb to idleness with a probably dependent upon a complex mix of factors, including the following.
*Their personality: lazy dwarves go idle more often
*The number of the item in the stockpile in relation to the settlement population: dwarves are less motivated to churn out surplus items than needed ones.
*Their happiness: unhappy dwarves are less motivated to work.
*The number of other citizens that are equal to or better than they are at a given task: dwarves are more motivated if there are other people who can do it better.
Idle dwarves are a nuisance because they do not just stop what they are doing, they hold onto both the capital, designations and the raw materials involved in a given task. Idle miners or woodcutters keep other miners or woodcutters from using their square or tree, idle carpenters take up their workshop and so on.
Banking and Money.
In order to overcome idleness one can use financial means. To do so you must create a bank, the presence of a bank enables the ability to buy and sell things at the shop and the bank uses up the accounting skill. Items that are sold (they may also be rationed) are given a value. A citizen that brings the requisite value over to the shop will buy the item, which as with rationed items is the only way the item can be had.
The shop can also buy items for a given value, this has a limited value in that it allows private property items that are not demand by their owners, that is usually inherited to be acquired. Bought items can be freely available from the stockpile, in which case haulers will simply stockpile it rather than keep it in the shop.
The bank tries to acquire as much currency in the fortress as is in the stockpiles until it reaches the limits of it's capacity. If it does then it will try to acquire chests and deposit them on the adjacent squares, filling them with currency. Individuals that have private property that they cannot otherwise store for whatever reason will also deposit their items in the bank.
A bank can be used to pay workers employed in the various professions a certain amount of value per any completed task involving that skill. As long as there any items sold in the shop that a citizen wants then the better paid a job is, the less they are prone to idleness. Citizens do not actually retrieve the money that they are paid immediately, instead each citizen has a bank account which keeps his or her money/stored item and the banker brings them the money or items that they wish to take out or deposits the money they are brought.
This ensures that labour is not spent moving stacks of coins around, a stack of coins is only taken out from the bank in order to spend at the shop and then whatever is left is deposited back into the bank account of that individual.