I drink a protein shake after working out - can you ever have too much protein?

Yes you can. The body can only put on a limited amount of protein in a day (varies with intake, disease state, etc). Dietary excess of protein requires can cause problems if there is any underlying decrease in kidney function (as may be seen with diabetes, aging, etc), can increase risk for kidney stones, dehydration (unless adequate h2o), liver abn. Balance studies show 0.8-1.0 gm/kg is plenty in good healt.
Protein intake. Excess protein intake is only a problem in persons with chronic renal disease, and even among them it is relatively rare. It is very important to maintain adequate fluid intake.
Yes. To add to dr kerr's response, protein is metabolized to Amino Acids and represents an extra acid load. There is some experimental evidence that extra protein may increase the risk for kidney stones (even if you don't have chronic kidney disease); most data in humans comes from ingesting extra animal protein and there is little to no info regarding protein supplement shakes.