There are a lot of factors to consider.
1. BMR: basal metabolic rate determines how fast your metabolism breaks down food into macros and how quickly your body burns calories. Hormones, genetics, age and your activity all play a part in your BMR. An 80yr sedentary female needs less protein than a 25yr old active male does.
2. Type of protein: everyone has heard of the different types of protein and their absorption rate and how much is absorbed into the body.
3. Other nutrients consumed at time of protein usage. This affects digestion rate because if there is fat mixed in, it takes longer to break down. Also the amount of ingredients has an affect. If you're taking a 50g shot of whey protein, the body will release it's enzymes and it'll be broken down quickly. You add peanut butter, oats and whey now your body has to send out different enzymes for the different types of carbs, fats and proteins involved.
My take: once again everything comes down to the individual. As I said hormones play a part so someone on test has a 30% increase of protein synthesis (I believe Viking said this in his post about getting the most out of test).
The studies they use, they only do a straight shot of protein, with no other nutrients so the body does excrete some to an extent. If you're having a steak with potatoes and broccoli, you have different carbs, different types of protein, different fats all vying for enzymes. Fats slow absorption rate, heck even carbs and protein slow down the absorption of other ingredients.
Genetics play a part. People with fast metabolism break down food quicker
Illness plays a factor. Most people don't realize this but if you're sick even just a head cold your protein metabolism goes through the roof. Whenever I get a head cold, I purée veggies and fruits and add 30g of whey protein concentrate and have it every tgree hours on top of my meals. My colds are gone in a day. This plays a factor too.
Finally I leave you with this link I all hope you'll read. It's about protein absorption. The interesting about it is that they had a controlled study. Every group was fed an over abundance of calories, all were sedentary and we're under direct supervision. One group was given 5% protein diet, 15% and 25%. All gained weight but the 25% group gained the most. However the 25% increased the most muscle mass out of all the group even though sedentary. The body will use the protein. May excrete some but there is not limit
http://www.t-nation.com/diet-fat-loss/protein-will-not-make-you-fat

The Key here is the Leucine content of foods. 3.5-4g Leucine is maximum to fully stimulate muscle protein synthesis. So with regards to foods it equates to ~ 50g protein (chicken, beef), 6 eggs, 32g whey protein. Hope this helps

The reality is we don't know the answer to how much we can use at a time, there's no scientific proof. I've experimented with this over the years and tried it lots of different ways. Personally I get in about 50g of protein in 8 meals totalling approximately 400g per day. I've consumed more without any noticeable effect, less in total doesn't seem to produce the same. If pushed for a definitive answer I would say 40-50g per meal is optimum for means better to eat less more regularly than big hits of protein less frequently.

any liquid protein should be spaced 4 hours apart. in the 4 hour space use food protein to cover the gaps as whey is very fast acting and will be digested at 15-20 grams per hour for 4 hours. I have whey in the morning and right before bed.

I was going to edit out what I wrote, my above information is wrong. the amount the body uses is dependant on the person and and what the body needs. if it works for you dont change anything because even science has no fkn clue.

You want to take in around 1 to 1-1/2grams per B.W so if you are 212 you have to at least take in 212grams of protein to grow. If you want to bulk up to 250lbs minimum in take 250grams. Try to go for the 1-1/2 grams anything the body won't use it will waste.