Is there a limit to how much protein I can put into my body before it stops delivering any real benefits or possibly causes damage?

Firstly there is NO scientific evidence that excess protein causes any damage. A recent conference in sports medicine recommended a protein intake of 1.7 gram per kilogram body weight for recreational weight trainers. So a 70kg person ought take in about 125g per day. This is best achieved in 3-4 servings of between 30-40 grams each, over the day. A serving can be supplied by: 2 tablespoons Perfect Protein, 4 tablespoons Weight Gainer in milk, or 1 chicken breast, 200g fish or meat, 4-5 eggs, 800g low fat yogurt.