I'm on the donor register but I certainly don't intend to become a donor of any organs at any time! I also hope I will never require anyone else's organs either. It isn't exactly like donating blood is it?
The way I see it is that no matter how many people register as donors, there will ALWAYS be a shortage of human organs for donation, and so there should be, as medical knowledge advances doctors get better at saving people who have suffered terrible injuries in road accidents, and road safety improves so there are fewer accidents.
But hopefully there will also be significant improvements in artifical organs so that donation from human to human is simply never required and no-one has to die to save someone else.
I am very nervous about any system which makes it obligatory for organs to be removed on death - I think this would lead to doctors being too ready to see a person as ready to be scrapped for parts - or anything which goes against the principle of organ donation being just that, a gift freely given with clear consent.