In reply to Quarryboy:
The average intake of protein for the average person does not need to be more than 0.8g/kg of body weight. However, when you are training, this would raise to around 1.5g/kg of body weight in the recovery period. However, if you eat more than this, e.g. 2g/kg of body weight, studies show there is no improvement in strength gains.
You can get all this protein through a balanced diet, studies show that if you increase your dietary intake, there is a linear increase in the amount of protein that you take in. However, this is as important as when you eat that protein. Food intake needs to be manipulated with the timing of the exercise and it is for this reason people take protein shakes. And this is because there is a window of opportunity after the exercise period where there a period to ensure maximum effect and the longer you live the smaller the effect. Therefore, people consume protein shakes straight after exercise to hit his window and its more convenient than taking a tuna or chicken sandwich to the climbing wall/outside or waiting until they get home.
So not only is what you eat is important but its when you eat iy and this is why athletes opt for protein shakes.