Whey protein is great when you use it after strenous muscle builiding activity, it has also been shown to decrease muscle remodelling if you use it before a workout too. It is digested extremely quickly so after a hard workout it helps to build muscle mass and strength. It is also good to have some slow digesting protein on board as well that will kick in to help with muscle repair after the whey protein has done its job. If you want to build muscle or preserve muscle while weight training or other muscle building exercises whey protein is great

As for being hard on the kidneys that applies to someone that is going through renal failure. There have been cultures that have survived on a diet of mainly meat and fat and have survived very well throughout the ages. If you are on the list for a transplant or undergoing kidney failure then you should probably avoid protein as well as a lot of other things. Of course if your kidneys have already conked out then the problem is the your probably not getting enough protein. A much bigger concern for kidney failure is being overweight and having high blood pressure. If you keep yourself fit and don't go overboard you should not have a problem with your kidneys.

Eat the protein that you would normally eat in a day and substitute the whey for some of it. If you are only into eating natural foods then you should stay away from whey because it is highly processed very pure form of protein. If you want a more natural source of whey try cottage cheese.

The only side effect I have noticed is that I put on muslce easier and I get zits on my chest and shoulders.

If you want more info look for some scientific meta analyses done on whey protein, there are some informative ones out there.