I guess when it comes to it though the decision has to be made whilst your heart is still beating and you're still breathing, but you are brain dead. Under these circs I can see why the decision is more difficult. Dh and I are both potential donors, and I would want the same for the ds's, but to have to make that decision when you're still fighting for hope...
As for the register, I was astounded to read on the BMA site that the register is not routinely referred to. Also Donor cards are only useful if you carry them on your body - if they're in your handbag the paramedics may not retrieve that. Hence the importance that your next of kin/close relatives know your wishes. They can act on those wishes whether or not you are registered.
Janh, I would also not refuse a transplant for my children (I am a supporter of opt-in). I think that there are other ways of increasing available donors, and ensuring that we have a joined up transplant system. I am concerned that the views and rights of certain ethnic/religious groups could be seen to be trampled upon (eg Muslims wish to be buried by sundown, and there is a concern that donation could prevent this - this has been clarified not to be the case by the Muslim council). The current law does not require registration anyway, and it is more important that the enxt of kin knows your wishes. I think that greater awareness and specific training for the staff approaching relatives would be helpful.
Not strictly relevant, but I had an emergency c/s with ds1, and an SHO was trying to get my consent as I was being taken to theatre. He made such a bad job of it, that I asked to speak to someone else, as on the basis of what he was saying I was not going to consent and wanted to know what alternative there was! The registrar reassured me in seconds! (During my second pregnancy I was "accidentally" consented for a hysterectomy!).