The FDA recommends 65 grams a day for people consuming 2000 calories and 80 grams a day for those consuming 2500.
People looking to increase muscle mass and doing intensive strength training or athletics will need slightly more than recommended. Hold on there champ! You think this means you need to eat more protein? Chances are, you, an average English-speaking person, already consume enough protein to meet these elevated levels! Spend a day recording how much you eat and of what, you'll probably find you already eat enough protein.
Generally, the largest protein recommendation ever supported by a controlled study is 1.6 grams of protein per kilogram of lean body mass, or ~.73 grams protein/pound of lean body mass.
So a 160 pound person of 10% body fat doing extensive strength training would benefit from how much protein?
160*.9= 144 pounds of lean body mass.(mass which is not fat) 144*.73= 105 grams of protein a day.
Bodybuilding magazines will have you believe you need much, much more protein, and will pull out folklorical numbers of "1 gram per pound of body mass" or even "2 grams per pound of body mass". These figures are purely anecdotal and there's no scientific evidence to support that people on equal calorie diets who consume much more protein gaining muscle mass faster as compared those who consume the 1.6 g/kg recommendation.
That being said, consuming a bit more than the 1.6g/kg recommendation, while ineffective at building muscle mass, probably won't be harmful. While some studies have linked extremely high protein consumption (greater than 400 grams a day!) to kidney troubles, there generally doesn't seem to be much evidence that a slightly elevated protein diet is harmful.
On the other hand, consuming excess protein will replace calories in your diet that could have been "used" on fruits, vegetables and whole grains. Many sources high in protein are also high in saturated fat and cholesterol, such as beef or pork. Consuming more of these sources for excess protein means you'll be consuming unneeded junk, heightening the risk of a heart attack. Be sure to choose healthier sources of protein, such as lean chicken, turkey, egg whites, skim dairy products or soy. Remember that protein contains 4 calories per gram, so consuming an excess protein that isn't burned as energy or used in the muscle will be converted to fat.