i think it is a good idea to donate organs. i have known 2 people who died early because they needed a liver transplant. It was heart breaking to see what the families went through in Pakistan. One family sold everything and borrowed heavily so they coulld go china and get a transplant it was unfortunately never meant to be as he passed away from a viral infection before he could get the liver.
I personaly think it has to do with what the persons intention is, and people forget Allah is merciful and understanding. From my understanding the objection for organ donation and post mortum is that your soul feels pain through these processes, that is why you have to be washed carefully and with respect.