I have been involved in an on-line debate with colleagues recently about the merits (or otherwise) of a law in favour of presumed consent for organ donation in the UK.
At present we have a system of opting in. Some of us would like to see the law switched to one of opting out. Indeed, such presumption of consent for organ donation is the current stance of the British Medical Association.
According to the transplant agency, NHS Blood and Transplant (NHSBT) there are currently an average of 7,500 people on th waiting list for transplant and, each year, about 1000 people die for want of a transplant.
The number of oragns available for transplant is falling. In part this is due to welcome things like improvement in road safety or more effective management of head injury or cerebral haemorrhage, etc.
But there are still a significant number of potentially useful organs lost each year because the wishes of the person who could be a potetial donor are unknown. They have not registered as organ donors and they have not told their families of their wishes.
A change to presumed consent would allow these organs to be used unless the person had opted out or made it very clear to their family that they did not wish to donate.
Of course, in the end of the day, this all boils down to a problem of ethics.
But ethics are fickle and often offer only a subjective assessment. So, for example, I think many of the big pharmaceutical companies are completely unethical - you may disagree or not but it doesn't stop both of us using the medicines they develop and manufacture. So are we being ethical or unethical?
The point of any ethics committee must be to look at both sides. The most unethical thing they could do would be not to listen to both sides. 
Some feel a default in favour of taking organs (i.e. presumed consent) is unethical. But is it really unethical taking organs from someone who has not expressed a view against that and, by virtue of being dead, no longer has a use for these organs or is it ethical that through a lack of presumed consent in this country we have let thousands of people who could have benefited from these organs die? Is the loss of two lives more ethical than one life lost, one life saved?
Organs could only be taken when a decision has been reached that a person is dead and that life support systems are to be switched off.
I would support a change in the law to presumed consent for competent adults provided that it was well sign-posted in advance and that opting out was made as easy and freely available as possible in shops, libraries, banks, post offices, health centres, etc.
In the meantime I think it is the ethical responsibility of those of us who work in healthcare to encourage our patients to sign up for the current opting in system.
If you haven't done so yourself you can do so here:

http://www.organdonation.nhs.uk/ukt/RegistrationForm.do