Let me start of by saying that I donate blood every 2 months, platelets every 4-6 weeks, and I am on the bone marrow list. In fact, a few months ago I was a match for a 12 year old who needed bone marrow, but in the end, they found someone closer to him to donate. I also am CMV negative, which means that my blood/platelets can be given to infants. So because I am CMV negative, and not many CMV negative donors donate, I donate as much blood as possible.
With that said, I am not a organ donor. I don't mind having my organs donated after I have died, but there has been countless of articles and reports over the years citing that when doctors find out a patient is a organ donor, they don't do everything possible to save the patient. In the end, regardless if it's true or not, I want to make sure a doctor saves me for me, not for my organs. But I have written instructions that allow my next of kin to donate my organs after I've been declared dead.