Depending on the room and what you use it for is how you really should decide number of circuits. If it is an average size family room with a tv and some lights one is enough. If you have a more extensive entertainment system put that on a circuit. If you have a computer area put that on a 20 amp circuit. Also code is not really every 6 feet. It is written so you wont be more than 6 feet from an outlet. Example, from a door measure 6 feet, continue along the wall, if it is unbroken by a doorway, 12 feet to next outlet, then 12 again. This is just the minimum and it is usually best to layout with the rooms use in mind. Just remember that you can not be more than 6 feet from an outlet.

The number of outlets per circuit depends on anticipated usage, not a general rule. You can put as many outlets on a circuit as you want (over a hundered if necessary, although that would be an odd case), but you cannot USE them all at the same time without overloading the circuit. For instance, only ONE outlet might use all the ampacity available in a circuit: say, for a range, A/C/ unit, computer and accessories, dishwasher, etc. In other cases, you can literally put twenty outlets on one circuit so as to be flexible as to where the three or four low-amp appliances (lamps, clocks) go in the room, but only use two or three of the outlets at a time. Outlets do not use up current, appliances do, so you can put as many outlets as you need/can use on a circuit

Electrical codes require an outlet every twelve feet, not as a guide to how many outlets you should have in a room, but so as to minimize the amount of exposed cord that runs in a room. Locating an outlet every twelve feet means that an appliance will not be more than 6 feet from an outlet at any spot along a wall.

As such, the number of outlets per circuit depend on the particular circumstance, not some general rule. A Kitchen can get six circuits that run to just one outlet (one for the dishwasher, one for the microwave, one for the garbage disposal, one for the range, and two for the outlets around the kitchen), whereas the rest of the house can survive on two or three other circuits. If you have large stereo equipment or lots of computer equipment, you might want to add a circuit or two for each one.

Thus, the rule is to roughly anticipate how much energy that you will use on each circuit, and plan accordingly. To just meet Code for outlets that you do not plan to use, you can use just one circuit for all of them.