I do not recommend that "Do Not Resuscitate" orders be made routinely outside a hospital setting. If someone is in hospice care then DNRs are appropriate at home. In a hospital setting, DNRs are very useful.
Having a DNR will keep extraordinary means from being used. One thing to remember, especially in the elderlty, is that CPR may well break bones which in turn can cause other complications. Most hospitals will allow some mild efforts to be made to keep you alive, such as administration of drugs that stimulate the heart even with a DNR in place, but that must be specified in the order. These are issues to be discussed with your physician, the earlier the better.
I do not recommend DNRs at home because if you are able to live at home and do not have hospice care, then I believe that there are too many variables to decide that no matter what you will not be resuscitated. It is far better to have the person that holds your medical power of attorney make that decision based on the circumstances at the time. Again, this is a personal decision and there is no correct answer, only what you want.
DNRs are only useful if those taking care of you know that you have one. In the hospital, this is not a problem usually. You must have the DNR at hand, if it is to be used at home. If emergency services are summoned to your home, their job is to keep you alive. Whether or not they will honor a DNR will depend on the law of your state. Many in hospice are told not to call emergency services in a crisis, but instead call hospice. This avoids the issue entirely.
Finally, life support can be removed. Even if you do not have a DNR or it has not been used or it has been ignored, you can make the decision to withdraw life support, or if you are not capable of making decisions, the person that holds your medical power of attorney can make that decision.