Here is a link to the National Institutes of health info for physicians. I found some info that indicates that 0.8 grams of protein per KG (2.2 pounds) is sufficient for normal body functioning. That works out to about .4 grams per pound. Since body builders do about 1 - 1.5 grams per pound, 0.4 should be fine for the average Joe or Josephine.
How do you keep track of how much protein you are taking in? I use a program called Diet Power but there are some free apps out there including one on Livestrong.