"Doctors putting in less effort to save you (from a coma etc) if they think that you can help the sprog in the next ward etc"
I'm offended by this too.
Organ donation goes ahead in two circumstances;
1. Heart beating donation; this is when you have been declared brain-dead by two seperate brain-stem death tests. Just to spell this out a bit more; that's when your brain no longer works to control your basic body functions like breathing. Causes of this state can be massive head trauma or major cerebral bleeding.
In other words, you are dead, but your heart is still pumping blood around your body.
2. Non-heart beating donation; this is rather newer, but essentially involves waiting for you to die, then taking you to theatre quickly to allow organ donation.
In neither case is there any attempt made to 'hurry things along', and no attempt made to provide less care because you may be a potential donor.
In many ways, it's far easier for everyone if you are not a donor; it's a major undertaking, and a difficult, stressful ballache to go through the whole setup, but it's worth it because it helps to save other peoples lives.