CPR certifications are really only to demonstrate to an employer that you've completed a CPR class. CPR certifications are largely unregulated, which means that almost anyone can print a card and pronounce someone CPR certified. Because of the mess of CPR training programs, many employers and state EMS agencies only accept CPR certifications from what I call the Big Three organizations: American Heart Association, American Red Cross and the National Safety Council.
Unlike other medical procedures, there isn't much of a downside to CPR. It doesn't have a lot of side effects. CPR is only effective for cardiac arrest, when the heart either stops beating or is not beating strongly enough to flow blood to the body and brain. Victims of cardiac arrest need CPR or they will die. There's no way around it; if you don't do CPR, the victim will die. If CPR doesn't work, the victim will die. If you do CPR -- even if it isn't perfect -- the victim might survive.
So, if you and I are alone in a room and my heart stops beating, I want you to push on my chest. I don't have a chance without your help. Whether or not you have a card in your wallet that says you are CPR certified doesn't matter to me. If you don't happen to have a CPR certification, that's OK; I'll make you one when I wake up. You can even pick the color.
The most important thing to remember is don't stand there, do something! If a person is not responding to you, call 911. If the person is not breathing, push on his chest. Whether you know how to do traditional CPR or not; whether you have a CPR certification or not, you just might save a life.